Meted hyperpolarized noble gas dispensing methods and associated devices

ABSTRACT

Methods of dispensing meted quantities of hyperpolarized gas to form a hyperpolarized gas mixture include pre-filling a gas syringe with a quantity of non-polarized gas, then introducing the hyperpolarized gas therein while the non-polarized gas is held therein, and expelling both the hyperpolarized gas and non-polarized gas from the syringe. Methods of inhibiting the presence of oxygen in gas flow paths and extraction systems are also described.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of co-pending U.S. application Ser. No. 09/528,750 filed Mar. 20, 2000, which is a continuation-in-part of U.S. application Ser. No. 09,163,721 filed Sep. 30, 1998, now issued U.S. Pat. No. 6,237,363. The contents of these documents are hereby incorporated by reference as if recited in full herein.

STATEMENT OF GOVERNMENT SUPPORT

[0002] Certain of the inventions described herein were made with Government support under National Institute of Health Grant No. 7R44HL59022-03. The United States Government has certain rights in those inventions.

FIELD OF THE INVENTION

[0003] The present invention relates to equipment and methods used to remove or dispense hyperpolarized gases from containers. The invention is particularly suitable for dispensing sterile or pharmaceutical hyperpolarized gases for Magnetic Resonance Imaging (“MRI”) applications.

BACKGROUND OF THE INVENTION

[0004] Conventionally, MRI has been used to produce images by exciting the nuclei of hydrogen molecules (present in water protons) in the human body. However, it has recently been discovered that polarized noble gases can produce improved images of certain areas and regions of the body which have heretofore produced less than satisfactory images in this modality. Polarized Helium-3 (“³He”) and Xenon-129 (“¹²⁹Xe”) have been found to be particularly suited for this purpose. Unfortunately, as will be discussed further below, the polarized state of the gases is sensitive to handling and environmental conditions and can potentially rapidly decay from the polarized state.

[0005] Hyperpolarizers are used to produce and accumulate polarized noble gases. Hyperpolarizers artificially enhance the polarization of certain noble gas nuclei (such as ¹²⁹Xe or ³He) over the natural or equilibrium levels, i.e., the Boltzmann polarization. Such an increase is desirable because it enhances and increases the MRI signal intensity, allowing physicians to obtain better images of the substance in the body. See U.S. Pat. No. 5,545,396 to Albert et al., the disclosure of which is hereby incorporated by reference as if recited in full herein.

[0006] The hyperpolarized gas is typically produced by spin-exchange with an optically pumped alkali metal. The alkali metal is removed from the hyperpolarized gas prior to introduction into a patient to form a non-toxic and/or sterile composition. Unfortunately, the hyperpolarized state of the gas can deteriorate or decay relatively quickly and therefore must be handled, collected, transported, and stored carefully.

[0007] The “T₁” decay constant associated with the hyperpolarized gas' longitudinal relaxation time is often used to describe the length of time it takes a gas sample to depolarize in a given situation. The handling of the hyperpolarized gas is critical because of the sensitivity of the hyperpolarized state to environmental and handling factors and the potential for undesirable decay of the gas from its hyperpolarized state prior to the planned end use, i.e., delivery to a patient for imaging. Processing, transporting, and storing the hyperpolarized gases—as well as delivery of the gas to the patient or end user—can expose the hyperpolarized gases to various relaxation mechanisms such as magnetic gradients, contact-induced relaxation, paramagnetic impurities, and the like.

[0008] In the past, rigid containers have been used to transport the hyperpolarized gas from a polarization site to an imaging site such as a hospital. Unfortunately, these conventional transport containers can leave relatively large residual amounts of the gas in the container at the end use point. For example, absent active pumping (which generally introduces unacceptable depolarization to the hyperpolarized gas) an atmosphere of hyperpolarized gas typically remains in the transport vessel, in equilibrium with the ambient air pressure. As such, a larger volume of gas is typically transported to the imaging site to provide the volume desired for clinical use. Unfortunately, the hyperpolarized gas is relatively expensive to produce and this wasted residual gas can disadvantageously escalate the cost of the hyperpolarized product even further. Further, as noted above, conventional pump delivery systems which attempt to extract the gas from the transport container can cause the polarization of the hyperpolarized gas to rapidly decay, thereby limiting the life of the product and providing potentially severe time constraints in which successful clinical imaging can be performed.

[0009] Further, bag containers have also been used in the past to administer hyperpolarized gas to a subject via inhalation. Unfortunately, the quantity of gas actually dispensed into the bag can vary. Therefore, it can be problematic, especially when blending hyperpolarized gas with a buffer gas, to provide reliable repeatable concentrations and/or quantities of the inhalable hyperpolarized gas or gas mixtures over a plurality of doses. In addition it may be desirable to use different amounts of gas or gas mixtures as well as different sized dose containers, patient to patient.

[0010] For example, it may be beneficial to provide different known concentrations of hyperpolarized gases (25%, 50%, and the like) within a relatively constant overall volume of inhalable gas mixture such as a 1 or 1.5 liter volume (the remainder of the mixture being formed by suitable buffer gases). That is, it is often desirable to have a subject inhale a sufficient quantity of the hyperpolarized gas mixture to either partially or substantially “fully” inflate the lungs. For image calibration and/or regulatory agency guidelines of human or animal administered hyperpolarized gas, it can be desirable to provide reliable doses of predetermined inhalable volumes of the hyperpolarized gas mixture. Unreliable concentrations can, unfortunately, yield varying signal intensities, dose to dose. On the other hand, dispensing only hyperpolarized gas (no buffer gas) can be more costly, and unnecessary from an image viewpoint, as successful images can be obtained with lower concentrations of hyperpolarized gas.

[0011] Accordingly, there remains a need to provide improved extraction systems and containers to reduce the depolarizing effect of the extraction system, to relatively efficiently deliver the hyperpolarized gas to the desired subject, and provide more reliable concentrations and/or dosages of hyperpolarized gas.

OBJECTS AND SUMMARY OF THE INVENTION

[0012] In view of the foregoing, it is an object of the present invention to provide improved methods to extract hyperpolarized gases from polarization cells or vessels, collection, and transport vessels in a way which reduces the de-polarization of the gas attributed thereto.

[0013] It is another object of the invention to reduce the residual amounts of hyperpolarized gas in collection vessels or transport vessels at the end use site.

[0014] It is an additional object of the present invention to provide improved gas dispensing and metering methods and systems which allow more reliable dose quantities of hyperpolarized gases and/or concentrations of hyperpolarized gas mixtures to be dispensed.

[0015] It is yet another object of the invention to provide improved gas dispensing methods and associated containers and apparatus to reduce any degrading effect that the dispensing may have on the polarized life of a hyperpolarized product so that the hyperpolarized product retains sufficient polarization at the end use site to allow effective imaging at delivery.

[0016] It is still another object of the present invention to provide dual purpose transport containers which are configured to both collect and transport the hyperpolarized gas.

[0017] It is another object of the present invention to provide improved dose metering of the hyperpolarized gas into containers in a manner which reduces depolarizing activity associated with the dispensing and delivery of the hyperpolarized gas to a subject.

[0018] It is yet another object of the invention to provide methods and apparatus which can reduce the de-polarizing effects on the hyperpolarized state of the gas attributed to active dispensing of the gas from a polarization cell, collection, or transport vessel.

[0019] It is another object of the present invention to provide improved methods for inhibiting the introduction of oxygen into gas extraction systems or hyperpolarized gas flow paths.

[0020] It is an additional object of the present invention to provide a masking method, which inhibits the direct contact of hyperpolarized gas with a potentially de-polarizing material or surface.

[0021] It is another object of the present invention to provide a polarization verification method which can identify the expiration date of the hyperpolarized gas externally so that hospital personnel can visually determine the status of the gas prior to delivery to a patient.

[0022] These and other objects are satisfied by the present invention which is directed to hyperpolarized gas extraction systems, methods, and associated containers which are configured to remove or extract the hyperpolarized gas from a container and reduce the amount of residual gases unrecovered therefrom in a way which reduces the depolarization of the hyperpolarized gas. In particular, a first aspect of the present invention is directed to a method for extracting a quantity of hyperpolarized noble gas from a container which includes directing a liquid into a container holding a quantity of hyperpolarized gas therein. The liquid contacts the hyperpolarized gas and forces the gas to exit the container separate from the liquid into an exit path operably associated with the container, thereby extracting the hyperpolarized noble gas from the container. In a preferred embodiment, the liquid comprises water which has been sterilized and partially, and more preferably, substantially de-oxygenated and/or deionized.

[0023] Another aspect of the present invention is directed towards a method similar to that described above, but this method introduces a quantity of fluid (such as gas or liquid) into the container to push the hyperpolarized gas out of the container. The liquid aspect is similar to that described above.

[0024] In one embodiment, wherein the fluid is a gas, the gas is preferably non-toxic and suitable for inhalation by a patient. As such, the extraction gas can mix with the hyperpolarized gas to form a hyperpolarized gas mixture as it exits from the container.

[0025] In another embodiment, the hyperpolarized noble gas exits the container separate from the extraction gas. In this embodiment, the extraction gas has a density which is substantially different from the hyperpolarized gas. For example, for ¹²⁹Xe, the extraction gas is preferably selected so that the hyperpolarized gas has a density which is greater than the extraction gas so that the extraction gas has a density which is less than the hyperpolarized gas. In this embodiment, the exit path is preferably positioned on the bottom portion of the container during the extraction while the extraction gas is introduced into the top portion of the container. This allows the heavier ¹²⁹Xe to exit out of the bottom of the container while the lighter weight extraction gas remains therein.

[0026] In another embodiment, the hyperpolarized gas is ³He, and the extraction gas is preferably selected such that it has a density which is greater than that of ³He. In this embodiment, the exit path is preferably positioned on the top portion of the container while the extraction gas is introduced into the bottom of the container. As such, the lighter ³He exits from the top of the container while the heavier extraction gas remains in the container.

[0027] In an additional aspect of the present invention, the extraction method includes engaging a gas transfer source with the container and drawing a quantity of hyperpolarized gas from a container such that the gas is controllably removed therefrom. In a preferred embodiment, the gas transfer source is a syringe that is inserted into the sealed exit path (via an access port) of the container to remove the hyperpolarized gas therefrom. Preferably, the gas transfer source is configured with gas contact surfaces which are friendly to the hyperpolarized state of the gas, i.e., coated with or formed of materials which do not cause excessive depolarization or which inhibit depolarization.

[0028] In certain embodiments, a quantity of non-polarized buffer gas into the syringe prior to introducing the hyperpolarized gas therein such that the non-polarized buffer gas is held in the chamber during the hyperpolarized gas introduction therein and the plunger is translated a first distance in the syringe away from the port in response to the quantity of non-polarized gas received therein and second further distance in response to the additional quantity of hyperpolarized gas introduced therein. The syringe can be pre-filled with a quantity of a desired buffer gas such as nitrogen and then filled with the hyperpolarized gas. Together, the plunger of the syringe can force the gases from the syringe chamber into a desired receiving line or container.

[0029] Another embodiment of the present invention is directed to methods of preparing a hyperpolarized gas extraction system to inhibit the presence of oxygen therein. The method includes: (a) introducing a quantity of inert noble purge gas into a gas flow path of a gas extraction system; (b) evacuating the flow path of the gas extraction system; (c) repeating the purging and evacuating steps; (d) then introducing additional purge gas into the gas flow path of the extraction system until the pressure therein is at about or above atmospheric pressure so as to inhibit oxygen from entering therein; and (e) subsequently (such as 10 minutes to about 2-4 hours or more later) introducing a desired quantity of hyperpolarized gas in the flow path of the extraction system.

[0030] Another aspect of the present invention is directed to a method of masking the potentially depolarizing effects of internal components or surface areas associated with the container. This method includes introducing a quantity of fluid (preferably a liquid) into the container and covering at least one predetermined exposed internal surface of the container with the fluid (liquid) to inhibit direct contact between the internal surface and the hyperpolarized noble gas, thereby masking the exposed surface with a fluid (liquid) to inhibit the depolarization of the gas in the container. In a preferred embodiment, the container is oriented to direct the masking fluid (liquid) into the desired area and the predetermined area includes covering a valve or seal in fluid communication with the container.

[0031] Yet another aspect of the invention is directed to a method of decreasing the residual amount of hyperpolarized gas remaining in the container when not using an active pumping or removal system. The method includes introducing a quantity of hyperpolarized noble gas into a small container (preferably less than about 500 cm³, and more preferably less than about 200 cm³) at a pressure of about 3-10 atm. The container is then sealed and transported to a use site remote from the polarization site where the container is opened to release the gas by allowing the container to depressurize to ambient pressure. This is a high pressure, low volume container/method which decreases the amount of residual gas left in low pressure, relatively high volume containers typical of conventional delivery methods/containers. This method is particularly suitable for ³He as higher pressures introduced to the hyperpolarized ³He still yield relatively long T₁'s.

[0032] An additional aspect of the invention is directed to a method of extracting hyperpolarized gas from a container by positioning a resilient member in fluid communication with the internal chamber of the container holding hyperpolarized noble gas. The resilient member is then expanded to extend into the container and contact the hyperpolarized gas. The gas is forced to exit the container away from the expanded resilient member. Preferably, the resilient member is sealed to the container to prevent the fluid used to expand or inflate the resilient member from contacting the hyperpolarized noble gas. Also, it is preferred that the resilient member be formed from or coated with a material which is friendly to polarization of the gas in the container. Stated differently, a material which is (substantially) not depolarizing to or which inhibits depolarization associated with surface contact with the hyperpolarized gas.

[0033] Another aspect of the present invention is directed to improved containers for processing and transporting hyperpolarized gases. In one embodiment, the container comprises a chamber and a quantity of hyperpolarized gas disposed therein. The container includes a resilient member which is positioned to be in communication with the hyperpolarized gas in the chamber. The resilient member has a first collapsed position and a second expanded position. When in the second position, the resilient member extends into the chamber a further distance relative to the first position. Preferably, the resilient member expands and retracts responsive to fluid introduced into an inlet port operably associated with the resilient member. Also, it is preferred that the resilient member is sealed such that it inhibits any expansion fluid from contacting the hyperpolarized gas. In operation, the expansion of the resilient member pushes/forces the hyperpolarized gas to exit the container, thereby actively forcing the hyperpolarized gas out of the container. Advantageously, this configuration can reduce the residual amounts of the gas left in the container while also minimizing potentially depolarizing interactions attributed to the active removal apparatus.

[0034] In an alternative embodiment, the container includes a hyperpolarized gas holding chamber and a quantity of hyperpolarized gas disposed therein. The container also includes an access port which is in fluid communication with the holding chamber and which is resiliently configured to receive a portion of a syringe therein. Preferably, the container also includes a valve and an externally accessible connector, such as a lure or septum type connection, which provides an “air-tight” seal for drawing the hyperpolarized gas from the container in a manner which reduces the possibility of the introduction of air therewith. Preferably, the syringe plunger and body and septum are formed from or coated with polarization friendly materials. Advantageously, controlled amounts of the gas can be removed from the transport vessel and conveniently be delivered to the patient by simply reversing the plunger to inject or deliver the desired quantity of hyperpolarized gas without complex machinery and the like. Additionally, masking liquid can be used in the container as noted above.

[0035] In an additional embodiment, the container comprises a gas holding chamber, a quantity of hyperpolarized gas, and two ports (an inlet port and an outlet port) in fluid communication with the chamber. The inlet and outlet ports are positioned on different sides of the chamber. Preferably, the two ports are radially misaligned and positioned at least 90 degrees apart from the other. It is also preferred that the two ports be offset relative to the other. For example, in one embodiment (during extraction of the gas) the exit port is above the inlet port. Similarly, in another embodiment, the inlet port is above the exit port.

[0036] The containers or transport vessels are preferably configured to reduce surface or contact depolarization by forming a contact surface of a material of a thickness which acts to minimize any associated surface or contact depolarization. In addition, the outer layer is preferably configured to define an oxygen shield overlying the inner layer and is configured to minimize the migration of oxygen into the container. Suitable materials and thicknesses and the like are described in U.S. Pat. No. 6,128,918, to Deaton et al., filed Jul. 30, 1998, entitled Containers for Hyperpolarized Gases and Associated Methods. The contents of this patent are hereby incorporated by reference as if recited in full herein. The container material can comprise one or more of a high-purity metal film, high-purity impermeable glass, high-purity metal oxide, and high-purity insulator or semiconductor (for example, high purity silicon).

[0037] It is additionally preferred that the container use seals such as O-rings which are substantially free of paramagnetic impurities. The proximate position of the seal with the hyperpolarized gas can make this component a dominant factor in the depolarization of the gas. Accordingly, it is preferred that the seal or O-ring be formed from substantially pure polyethylene or polyolefins such as ethylene, propylene, copolymers and blends thereof. Of course, fillers which are friendly to the hyperpolarization can be used (such as substantially pure carbon black and the like). Alternatively, the O-ring or seal can be coated with a surface material such as LDPE or deuterated HDPE or other low-relaxivity property material or high purity metal.

[0038] Another aspect of the present invention is directed towards a method for improving the transfer efficiency of the hyperpolarized gas such as from the polarization cell in the hyperpolarization apparatus. In certain embodiments, the method comprises the steps of positioning a chamber in fluid communication with the polarization cell, directing a quantity of hyperpolarized gas out of the polarization cell and into the chamber, and cooling the chamber to improve the transfer of hyperpolarized gas from the polarization cell. The cooling step can cool the container substantially, such as below the freezing point of water, and more preferably to the temperature of dry ice (195 K.), and most preferably to cryogenic temperatures (such as by exposing the chamber to a bath of liquid nitrogen (77K.)). In one embodiment, the hyperpolarized gas is ³He. In another embodiment, the chamber is closed or configured to capture all the gas exiting the polarization cell. The cooling of the chamber can increase the pressures and volumes of gas received into the chamber (and thus out of the polarization cell), improving the transfer efficiency thereby.

[0039] Still another aspect of the present invention is a method of identifying the hyperpolarization state of a quantity of hyperpolarized gas (such as at a use-facility or site). The method includes positioning a container having a quantity of hyperpolarized substance in a magnetic field and determining the polarization level of the hyperpolarized substance in the container. An externally visible indicia of polarization, i.e., an identifying mark such as a use-by date is affixed to the container. The identified container is then protected from de-polarizing factors. For example, storing the identified container in a stable magnetic field. Advantageously, this identification can preclude or minimize the delivery of inactive gases to a patient by indicating a shelf life associated with a desired level of polarization of the hyperpolarized substance in the container to hospital personnel. Preferably, the magnetic field has a low field strength, and the determining step includes transmitting a signal to the hyperpolarized substance in the container and receiving a signal back therefrom. The signal back corresponds to the hyperpolarization level of the substance in the container.

[0040] Another aspect of the present invention is a method of meting a quantity of hyperpolarized gas into a container. The method includes the step of providing an enclosed sealable gas flow path, the gas flow path extending between a hyperpolarized gas source and a first gas syringe, and between the first gas syringe and a sealable container different from the hyperpolarized gas source. The first gas syringe has a translatable plunger held therein and a port configured to receive gas into and expel gas from the syringe. A quantity of hyperpolarized gas is released in gaseous form from the hyperpolarized gas source such that it flows into the gas flow path. The hyperpolarized gas is directed in the gas flow path into the first syringe and received in gaseous form into the first syringe. The plunger is translated a distance in the first syringe away from the port in response to the quantity of hyperpolarized gas received therein. Subsequently, the plunger is advanced a desired distance in the first syringe toward the port to direct a desired quantity of hyperpolarized gas in gaseous form from the first syringe into the gas flow path and then into the sealable container thereby meting a desired amount of the hyperpolarized gas into the sealable container.

[0041] In certain embodiments, a buffer gas can be similarly meted into the sealable container (from a gas syringe). The same syringe as used for the hyperpolarized gas dispensing can be used to dispense or mete the buffer gas. Alternatively, a separate syringe (i.e., a dual syringe system) can be used. In any event, a more reliable predictable quantity of hyperpolarized gas can be meted into the sealable container to provide for more reliable quantities and/or concentrations of the hyperpolarized gas and the buffer gas mixture over conventional procedures.

[0042] A related aspect of the present invention is a hyperpolarized gas dose-meting apparatus. The apparatus includes a hyperpolarized gas source, a first valve operably associated with the hyperpolarized gas source and a first gas syringe in fluid communication with the hyperpolarized gas source. The apparatus also includes a first enclosed flow path extending between the hyperpolarized gas source and the first syringe, a second valve operably associated with the first flow path positioned intermediate the hyperpolarized gas source and the first syringe, and at least one receiving container in fluid communication with the first gas syringe. The apparatus additional includes at least one second enclosed flow path extending between the first syringe and the at least one receiving container, at least one third valve operably associated with the receiving container; and at least one release mechanism operably associated with the second flow path positioned in the second flow path upstream of the third valve and the receiving container to allow the receiving container to be released and sequentially replaced with a second receiving container thereat.

[0043] In one embodiment, the hyperpolarized gas source is a polarization cell in a polarizer unit. The apparatus can include a second syringe holding a quantity of buffer gas therein, a third enclosed flow path extending between the second syringe and the receiving container, and a fourth valve operably associated with the third enclosed flow path. The first and second gas syringes can be sized to hold from about 0.5-2 liters of gas therein.

[0044] The hyperpolarized gas dose-meting apparatus may also include a holding apparatus configured and sized to hold the first and second syringes therein in side by side alignment. The at least one receiving container can be a single (of sequentially filled containers) or a plurality of containers. In one embodiment, the receiving container has collapsible walls.

[0045] An additional aspect of the present invention is directed to a hyperpolarized gas dose-meting gas syringe holding apparatus. The syringe holding apparatus/assembly comprises a first gas syringe having a body with a length, a port formed in a first end portion thereof, and a translatable plunger held therein. The syringe and the plunger having hyperpolarized gas-contacting surfaces formed of polarization friendly materials. The syringe includes externally visual indicia along the length thereof allowing a quantitative assessment of the gas volume held therein. The apparatus further includes a holding shell configured and sized to hold at least the first syringe therein. The holding shell has opposing first and second platform portions. The first platform portion includes an aperture formed therein for allowing the plunger to translate therethrough.

[0046] In another embodiment, the apparatus also includes a second syringe, and the holding shell is configured to hold the second syringe substantially alongside the first syringe therein. The syringes may be substantially the same size and shape (capable of holding from about 0.5-2 liters or more of gas therein) and the holding shell is configured to hold the first and second syringes in side by side alignment.

[0047] For each of the above, a magnetic field generator either comprising an electromagnet or a plurality of discrete permanent magnets can be arranged to provide (surround) the first syringe and/or the hyperpolarized gas flow paths/receiving container with a substantially homogeneous magnetic holding field. An NMR excitation coil can also be used to monitor the polarization level of the polarized gas at desired locations within the extraction system.

[0048] The methods and containers of the present invention can improve the relaxation time (i.e., lengthen the T₁) of the hyperpolarized gas such as by allowing active dispensing of the gas from a container in a manner which inhibits depolarization of the hyperpolarized gas. The methods and apparatus of the present invention can also allow for more predictable meting of the hyperpolarized gas so as to meet regulatory guidelines and/or provide more reliable concentrations or quantities of hyperpolarized gases/mixture, and, thus, provide suitable in vivo mammalian (preferably human) doses. Further, the active dispensing can reduce the amount of residual gases left in the container at the removal point, thereby improving the delivery efficiency.

[0049] The foregoing and other objects and aspects of the present invention are explained in detail herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0050]FIG. 1 is a schematic illustration of a xenon hyperpolarizer apparatus showing a container according to one embodiment of the present invention.

[0051]FIG. 1A is a perspective view of a helium hyperpolarizer system.

[0052]FIG. 2A is an enlarged plan view of the container shown in FIG. 1.

[0053]FIG. 2B is a schematic illustration of one extraction method according to embodiments of the present invention showing liquid extraction of hyperpolarized gas from the container of FIG. 2A.

[0054]FIG. 3 is a schematic illustration of another embodiment of a liquid extraction system showing an alternate container and a patient delivery bag according to embodiments of the present invention.

[0055]FIG. 4 is a schematic illustration of a liquid extraction system showing an alternative liquid source according to another embodiment of the present invention.

[0056]FIG. 5 is a graphical representation showing the signal strength of hyperpolarized ³He over time (the exponential decay constant of the gas) after contact with water.

[0057]FIG. 6A is a schematic representation of a container with liquid inserted therein in accordance with a masking method according to embodiments of the present invention.

[0058]FIG. 6B is a schematic representation of the container of FIG. 6A, showing the container oriented to dispose the liquid over the neck (valve area) of the container according to embodiments of the present invention.

[0059]FIG. 7 is a schematic representation of a gas extraction method according to embodiments of the present invention.

[0060]FIG. 8 is a schematic representation of a gas extraction method according to another embodiment of the present invention.

[0061]FIG. 9A is a schematic illustration of a gas extraction method and associated components according to embodiments of the present invention.

[0062]FIG. 9B is a schematic illustration of the release/delivery of the gas extraction method shown in FIG. 9A.

[0063]FIG. 10 is a schematic representation of a container with a resilient member and an associated expandable material extraction method according to embodiments of the present invention.

[0064]FIG. 11 is a schematic representation of the method and container in FIG. 10 showing the resilient expandable member in the container in an expanded position in the container according to embodiments of the present invention.

[0065]FIG. 12 is a schematic illustration of a patient delivery system according to embodiments of the present invention, the hyperpolarized gas being directed from the deliver vessel to an inhalation mask positioned on a patient.

[0066]FIG. 13 is a schematic illustration of a direct delivery method using the gas extraction method shown in FIG. 11.

[0067]FIG. 14 is a schematic illustration of a cryogenic cooling method according to embodiments of the present invention.

[0068]FIG. 15 is a schematic representation of a polarization determination or calibration station according to embodiments of the present invention.

[0069]FIG. 16 is a perspective view of a polarizer unit with an integrated optical pumping cell in fluid communication with a syringe-based meted gas dispensing system according to embodiments of the present invention.

[0070]FIG. 17A is a schematic illustration of a dual syringe-based meted gas dispensing system according to embodiments of the present invention.

[0071]FIG. 17B is a perspective view of one embodiment of a dual syringe configuration according to embodiments of the present invention.

[0072]FIG. 18 is a schematic illustration of a dual syringe-based meted gas dispensing system for filling a plurality of separate containers according to embodiments of the present invention.

[0073]FIG. 19 is a perspective view of a magnetic field generator positioned to enclose the hyperpolarized syringe (shown held in the holding apparatus) to provide a magnetic protective holding field to extend the polarization life of the hyperpolarized gas according to embodiments of the present invention.

[0074]FIG. 20A is a front perspective view of a single syringe device according to embodiments of the present invention.

[0075]FIG. 20B is a bottom perspective view of the device shown in FIG. 20A.

[0076] FIGS. 21A-21C are schematic illustrations of a sequence for dispensing measured doses of hyperpolarized gas mixtures according to embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0077] The present invention will now be described more fully hereinafter with reference to the accompanying figures, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Like numbers refer to like elements throughout. In the figures, layers, regions, components or features may be exaggerated for clarity. Also in the figures, broken lines, where used, indicates an optional feature.

[0078] For ease of discussion, the term “hyperpolarized gas” will be used to describe a hyperpolarized gas alone, or a hyperpolarized gas which contacts or combines with one or more other components, whether gaseous, liquid, or solid. Thus, the hyperpolarized gas described herein can be a hyperpolarized gas composition/mixture (preferably non-toxic such that it is suitable for in vivo introduction) such that the hyperpolarized noble gas can be combined with other noble gases and/or other inert or active components. Also, as used herein, the term “hyperpolarized gas” can include a product in which the hyperpolarized gas is dissolved into another liquid (such as a carrier fluid) or processed such that it transforms into a substantially liquid state, i.e., “a liquid polarized gas”. Thus, although the term includes the word “gas”, this word is used to name and descriptively track the gas produced via a hyperpolarizer to obtain a polarized “gas” product. In summary, as used herein, the term “gas” has been used in certain places to descriptively indicate a hyperpolarized noble gas which can include one or more components and which may be present in one or more physical forms.

[0079] Background—Hyperpolarization

[0080] Various techniques have been employed to polarize, accumulate and capture polarized gases. For example, U.S. Pat. No. 5,642,625 to Cates et al. describes a high volume hyperpolarizer for spin-polarized noble gas and U.S. Pat. No. 5,809,801 to Cates et al. describes a cryogenic accumulator for spin-polarized ¹²⁹Xe. The disclosures of these patents are hereby incorporated herein by reference as if recited in full herein. As used herein, the terms “hyperpolarize” and “polarize” are used interchangeably and mean to artificially enhance the polarization of certain noble gas nuclei over the natural or equilibrium levels. Such an increase is desirable because it allows stronger imaging signals corresponding to better MRI images of the substance and a targeted area of the body. As is known by those of skill in the art, hyperpolarization can be induced by spin-exchange with an optically pumped alkali-metal vapor or alternatively by metastability exchange. See U.S. Pat. No. 5,545,396 to Albert et al. The alkali metals capable of acting as spin exchange partners in optically pumped systems include any of the alkali metals. In certain embodiments, alkali metals used for this hyperpolarization technique include Sodium-23, Potassium-39, Rubidium-85, Rubidium-87, and Cesium-133.

[0081] Alternatively, the noble gas may be hyperpolarized using metastability exchange. (See e.g., Schearer L D, Phys Rev, 180:83 (1969); Laloe F, Nacher P J, Leduc M, and Schearer L D, AIP ConfProx #131 (Workshop on Polarized ³He Beams and Targets) (1984)). The technique of metastability exchange involves direct optical pumping of, for example, ³He without need for an alkali metal intermediary. Metastability exchange optical pumping will work in the same low magnetic fields in which spin exchange pumping works. Similar polarizations are achievable, but generally at lower pressures, e.g., about 0-10 Torr.

[0082] Generally described, for spin-exchange optically pumped systems, a gas mixture is introduced into the hyperpolarizer apparatus upstream of the polarization chamber. Most xenon gas mixtures include a buffer gas as well as a lean amount of the gas targeted for hyperpolarization and is preferably produced in a continuous flow system. For example, for producing hyperpolarized ¹²⁹Xe, the pre-mixed gas mixture is about 85-98% He, about 5% or less ¹²⁹Xe, and about 1-10% N₂. In contrast, for producing hyperpolarized ³He, a typical mixture of about 99.25% ³He and 0.75% N₂ is pressurized to 8 atm or more and heated and exposed to the optical laser light source, typically in a batch mode system. In any event, once the hyperpolarized gas exits the pumping chamber it is directed to a collection or accumulation container.

[0083] A 5-20 Gauss alignment field is typically provided for the optical pumping of Rb for both ¹²⁹Xe and ³He polarization. The hyperpolarized gas is collected (as well as stored, transported, and preferably delivered) in the presence of a magnetic field. It is preferred for ¹²⁹Xe that the field be on the order of at least 500 Gauss, and typically about 2 kilo Gauss, although higher fields can be used. Lower fields can potentially undesirably increase the relaxation rate or decrease the relaxation time of the polarized gas. As regards ³He, the magnetic field is preferably on the order of at least 10-20 gauss although, again, higher fields can be used. The magnetic field can be provided by electro or permanent field magnets. In one embodiment, the magnetic field is provided by a plurality of permanent magnets positioned about a magnetic yoke that is positioned adjacent the collected hyperpolarized gas. The magnetic field can be homogeneously maintained around the hyperpolarized gas to reduce field-induced degradation.

[0084] Referring to the drawings, FIG. 1 illustrates a xenon hyperpolarizer unit 10. As shown, the unit 10 includes a noble gas supply 12 and a supply regulator 14. A purifier 16 is positioned in the line to remove impurities such as water vapor from the system as will be discussed further below. The hyperpolarizer unit 10 also includes a flow meter 18 and an inlet valve 20 positioned upstream of the polarizer cell 22. A optic light source such as a laser 26 (typically a diode laser array) is directed into the polarizer cell 22 through various focusing and light distributing means 24, such as lenses, mirrors, and the like. The light source is circularly polarized to optically pump the alkali metals in the cell 22. An additional valve 28 is positioned downstream of the polarizer cell 22. Additional explanation of the hyperpolarizer is described in Cates et al., supra, and in U.S. Pat. No. 6,079,213, filed Dec. 12, 1997, entitled Methods of Collecting, Thawing, and Extending the Useful Life of Polarized Gases and Associated Accumulators and Heating Jacket. The contents of these disclosures are hereby incorporated by reference as if recited in full herein. In order to transport the hyperpolarized gas in a gaseous state, the hyperpolarized ¹²⁹Xe is preferably cryogenically accumulated in a cold finger or container 30 that is positioned in a cryogenic bath 43. The frozen polarized ¹²⁹Xe gas is then thawed out of the cold finger or container 30 and captured by a collection or transport vessel 50A positioned in fluid communication with the on-board exit tap 50.

[0085]FIG. 1A illustrates a preferred helium hyperpolarizer unit 10′. Similar to the ¹²⁹Xe hyperpolarizer unit 10 generally discussed above, the ³He hyperpolarizer unit 10′ polarizes the ³He in a polarization cell 22 and collects the gas at the gas exit tap 50 into the storage or transport container 50A. Certain of the plumbing of the helium device differs from the xenon apparatus, because the helium is batch process unlike the continuous process used to hyperpolarize xenon.

[0086] Prior to use in the unit 10, the storage containers 50A (and other storage, transport, or collection chambers) are preferably (repeatedly) purged and/or evacuated to remove oxygen, moisture, and the like. In certain embodiments, a rough vacuum pump is used to perform a first evacuation, then a high-purity gas is introduced into the container to purge residual contaminants. Additional evacuations can be performed such that the O₂ concentration is about 10⁻⁶-10⁻¹⁰ atm or lower. Of course, turbo-molecular pumps, cryopumps, and/or diffusion pumps (with or without heating) may also be used to treat or evacuate the vessel to remove any monolayers of moisture or water or other minute contaminants on the surface and thus further reduce contact-induced depolarization for the hyperpolarized gas.

[0087] Polarized Gas Relaxation Processes

[0088] Once hyperpolarized, there is a theoretical upper limit on the relaxation time (T₁) of the polarized gas based on the collisional relaxation explained by fundamental physics, i.e., the time it takes for a given sample to decay or depolarize due to collisions of the hyperpolarized gas atoms with each other absent other depolarizing factors. For example, ³He atoms relax through a dipole-dipole interaction during ³He-³He collisions, while ¹²⁹Xe atoms relax through N·I spin rotation interaction (where N is the molecular angular momentum and I designates nuclear spin rotation) during ¹²⁹Xe—¹²⁹Xe collisions. Stated differently, the angular momentum change associated with flipping a nuclear spin over is conserved by being taken up by the rotational angular momentum of the colliding atoms. In any event, because both processes occur during noble gas-noble gas collisions, both resulting relaxation rates are directly proportional to gas pressure (T₁ is inversely proportional to pressure). At one atmosphere, the theoretical relaxation time (T₁) of ³He is about 744-760 hours, and for ¹²⁹Xe the corresponding relaxation time is about 56 hours. See Newbury et al., Gaseous ³ He— ³ He Magnetic Dipolar Spin Relaxation, 48 Phys. Rev. A., No. 6, p. 4411 (1993); Hunt et al., Nuclear Magnetic Resonance of ¹²⁹ Xe in Natural Xenon, 130 Phys Rev. p. 2302 (1963). Unfortunately, other relaxation processes prevent the realization of these theoretical relaxation times. For example, the collisions of gaseous ¹²⁹Xe and ³He with container walls (“surface relaxation”) have historically dominated most relaxation processes. For ³He, most of the known longer relaxation times have been achieved in special glass containers having a low permeability to helium. U.S. Pat. No. 5,612,103 to Driehuys et al. describes using coatings to inhibit the surface-induced nuclear spin relaxation of hyperpolarized noble gases, especially ¹²⁹Xe. The contents of this patent are hereby incorporated by reference as if recited in full herein. Similarly, U.S. Pat. No. 6,128,918, and U.S. patent application Ser. No. 09/334,400 filed Jun. 16, 1999, describe gas-contact surface materials and associated thicknesses, O-ring, and valve or seal materials and/or coatings which are friendly to the polarized state of the gas, i.e., which can inhibit surface/contact-induced relaxation mechanisms. The contents of these documents are hereby incorporated by reference as if recited in full herein.

[0089] Once the hyperpolarized gas is collected, it is typically delivered to a hospital or end user. This means that either a hyperpolarizer unit is proximately stationed in the hospital so that the hyperpolarized gas can be delivered directly to the patient, or that the gas is transported from a central, albeit remote polarization site. The remote polarization station typically requires a longer T₁'s relative to an onsite apparatus to allow adequate shipping and transport times. However, a centrally stationed polarizer can reduce equipment and maintenance costs associated with a plurality of on-site units positioned at each imaging site. In any case, the hyperpolarized gas is typically removed from the collection container or transport vessel and dispensed to the patient via some patient delivery system temporally limited such that the hyperpolarized state of the gas at delivery is sufficient to produce useful clinical images.

[0090] Extraction Systems

[0091] It will be appreciated by those of skill in the art that certain of the descriptions herein are primarily directed to either a liquid or a gas, but that the methods of the inventions can use multiple types of fluids and are not intended to be limited to the specific description used herein. As such, as used herein, the term “fluid” includes liquids, gases, and blends and mixtures thereof.

[0092] A. Liquid Extraction

[0093] Turning now to the drawings, FIG. 2B illustrates one embodiment of a hyperpolarized gas extraction system according to the present invention. In this embodiment, a container 50A (FIG. 2A) is removed from the hyperpolarizer unit and transported away from the polarization site. The container is then prepared to release the gas therefrom. As shown in FIG. 2B, a liquid source 70 is attached to a liquid entry port 72. A valve 35 is opened and liquid is directed into the container 30. A valve 38 is opened to allow the hyperpolarized gas to exit the exit path 76. FIG. 2B shows an optional second valve 37 which can assist in holding degassed liquid in the container. As shown in FIG. 2B, during extraction, the container 50A is preferably oriented such that the gas exit path 76 is above the liquid entry port 72. In operation, the increasing liquid level contacts the hyperpolarized gas and pushes or forces the hyperpolarized gas out of the container 50A and into the exit path 76. It is preferred that the liquid level be adjusted so that the liquid remains in the container separate from the extracted gas, especially for gas inhalation applications. This method allows for substantially all of the hyperpolarized gas in the container 50A to be removed with minimal dilution and/or depolarization of the hyperpolarized gas.

[0094]FIG. 3 illustrates a liquid extraction system with a modified container 50A. In this embodiment, the container 50A has two ports; an inlet port 230 and an outlet port 234. As shown, the outlet port 234 is on a different (preferably opposing) side of the container and offset relative to the inlet port 230. As shown in FIGS. 6 and 9, an axis 200 drawn through the center of the container sections the container into four quadrants. Preferably, the inlet port 230 is positioned in one of the bottom quadrants and the outlet port 234 is positioned in the opposing top quadrant. Each of the ports 234, 230 is operably associated with a valve 235, 231 to control the release of the gas and introduction of the liquid, respectively. During extraction, this configuration allows the container 50A to be oriented such that the outlet port 234 is on a top end portion of the container and above the inlet port 230. As shown, the liquid source 70 preferably uses gravity to feed the liquid 70′ into the container. Of course, other controlled or active feed systems can also be employed (such as pumps, compression cuffs, syringes, and the like).

[0095] Referring again to FIG. 3, as illustrated, the inlet port 230 includes a connector 232 which allows the liquid source 70 to be attached to the container 50A. Similarly, the outlet port 234 includes a connector 236 which can attach to a patient delivery vessel 250. The patient delivery vessel 250 is preferably a collapsible bag. Of course, as an alternative to a patient delivery vessel 250, the gas can be directly routed from the outlet port/exit path 234 to the patient (such as to an inhalation mask positioned over a patient's nose/mouth FIG. 13, 255).

[0096]FIG. 4 shows another embodiment of a liquid extraction system. In this embodiment, the liquid source 370 is a syringe. As such, the extraction liquid 371 is inserted/injected via the syringe 370 into an access port 310 positioned in fluid communication with the container 50C. As shown, the access port 310 is positioned in an elbow 311 which is in fluid communication with the gas in the container 50C and is configured to receive a portion of the syringe therein. Preferably, the access port 310 is resilient in that it is configured with resilient material to receive the septum therein in a manner which provides an air tight seal. In one embodiment, the access port 310 is a lure-type connector. Also, preferably the access port is self-healing such that it forms an air-tight seal with the syringe when inserted therein and automatically collapses or closes to seal the port when the syringe 370 is withdrawn.

[0097] As noted, the liquid contacts the hyperpolarized gas. As such, for in vivo applications, it is preferred that the extraction liquid be selected so as to be non-toxic and non-depolarizing to the hyperpolarized gas. It is further preferred, for liquids which have a relatively high oxygen solubility value, that the liquid be processed to be more compatible to the hyperpolarized gas. For example, it is preferred that the liquid be at least partially de-oxygenated and/or partially de-ionized prior to introduction into the container or transport vessel with the hyperpolarized gas. It is more preferred that the liquid be sterilized and substantially de-oxygenated and/or substantially de-ionized. Other modifications and treatment processes can also be performed on the liquids to make them more polarization friendly. For example, certain elements of the liquids can be substituted or deuterated and the like. It is additionally preferred that the liquid be selected such that the hyperpolarized gas is substantially insoluble in the liquid. It is preferred that the solubility of the hyperpolarized gas in the fluid be less than about 0.2. For example, xenon has a solubility of about 0.14 in H₂O (with helium being about 0.01). In contrast, for example, xenon has a solubility of about 2.0 in hexane making this a poor choice for an extraction fluid for this gas (even aside from its toxicity issues).

[0098] Of course, a plurality of liquids can also be used as the extraction liquid, such as a liquid mixture, or blend whether miscible or immiscible. Tests indicate that one suitable liquid is water. Water is compatible and substantially non-depolarizing to both ³He and ¹²⁹Xe.

[0099] In one example, adding about 20 cubic centimeters of partially degassed water into the chamber of a 250 ml container changed the associated T₁ of the gas in the container from about 8 hours to about 5 hours. As shown in FIG. 5, the polarization decay curves observed from this test fit the exponential decay curve. This test supports the suitability/viability of this active extraction system. Preferably, immediately after the extraction is completed (especially when used with ³He), the extracted hyperpolarized gas maintains a T₁ equal to at least about 80% or more, most preferably, 90% or more of the value of the T₁ immediately prior to initiation of the extraction method (assuming a properly processed, cleaned, and appropriate transfer container).

[0100] B. Liquid as a Masking Agent

[0101] An additional aspect of the present invention is directed to using liquid as a masking agent in physical systems or containers which potentially contact the hyperpolarized gas. As is now understood, the effective T₁ of gas in a container is additive in relationship to the materials that the gas contacts. That is, the effective T₁ will increase nonlinearly according to the following equation.

1/T _(1 chamber)+1/T _(1 material)=1/T _(1 effective)   Equation 1.0

[0102] Therefore, the effective T₁ is dependent on the chamber surface area and material, as well as any other materials which contact the gas. By inhibiting the gas from contacting degrading materials, the effective T₁ can be extended or preserved.

[0103] As shown in FIG. 6B, a (predetermined) exposed internal surface 533 of the container 50D is covered with liquid. Preferably, the liquid 570 is selected such that it displays a greater compatibility with the hyperpolarized gas than the degrading contact surface or component (such as conventional O-rings, valves, seals, and the like) and is introduced into the container 50D to inhibit direct contact between the undesirable surface and the hyperpolarized gas. Advantageously, other properties typically attributed to the undesirable surface (seals, etc.) can be retained. Further, if used as shown to mask seals and the like, commercially available seals can be used without requiring specialized (and potentially costly) formulations of materials. This is because the liquid (or fluid) covers the surface or component, thereby masking the potentially depolarizing area from the hyperpolarized gas by contacting the gas with a material which has improved relaxivity relative to the undesirable surface or component. Also preferably, the liquid is chosen such that it is substantially non de-polarizing to the hyperpolarized gas (and resistant to hyperpolarized gas dissolution therein), so that it increases the length of the polarized life of the gas in the container over the life of the gas without the liquid mask. As discussed above, the liquid is also preferably non-toxic in that it contacts the (in a preferred embodiment, inhalable) hyperpolarized gas. For liquids which have high oxygen solubility, it is preferred that the liquid be at least partially de-oxygenated/de-ionized as discussed above. Further, one or more liquids can be used and the liquids may otherwise or additionally modified or processed as described above.

[0104] In operation, as shown by FIGS. 6A and 6B, a quantity of liquid is placed in the container 50D housing the polarized gas. The container 50D is then oriented such that the liquid in the container covers and thus inhibits the gas from contacting the valve 530 or other undesirable material or component, i.e., is positioned intermediate of the gas and the valve to mask the valve from the polarized gas. For example, in one test, fifteen cubic centimeters of de-ionized/de-oxygenated water were injected into a one-liter plastic bag with a valve thereon that had been previously filled with polarized gas. The bag was then positioned such that the water in the bag completely masked the valve from the polarized gas. The addition of water to the plastic bag increased the T₁ by about one hour.

[0105] C. Extraction Using a Gas

[0106] In this embodiment, a second gas is used to transfer the hyperpolarized gas from one vessel to another. Inasmuch as a preferred embodiment of the liquid transfer was described above, this description will be directed to the use of an extraction gas or extraction gas mixture (a plurality of gases) to transfer the hyperpolarized gas out of a container or transport vessel.

[0107] Turning now to FIGS. 7 and 8, two embodiments of a gas extraction system 600, 700 are shown. In these embodiments, the container 50C is the same as that described above, although, of course, the method and containers contemplated by this invention are not limited thereto. As shown, the container 50C includes the inlet and outlet ports 230, 234, respectively. In this embodiment, the extraction gas 670 is introduced into the inlet port 230 to contact the hyperpolarized gas in the container and force the gas out of the container through the outlet or exit port 234. As the extraction gas 670 contacts the hyperpolarized gas, it is preferred that it is non-toxic (so as not to contaminate the hyperpolarized gas) and substantially non-depolarizing to the hyperpolarized gas. Preferably, the second gas or extraction gas (or gas mixture) 670 has a substantially different density relative to the hyperpolarized gas. For example, N₂ would be suitable to use with both ³He and ¹²⁹Xe because it is inert, non-toxic, and its density is higher than that of ³He and lower than that of ¹²⁹Xe. Alternatively, helium is also inert and non-toxic and can be used to extract the ¹²⁹Xe. In any event, it will be appreciated by one of skill in the art that at 20° C., helium has a density of about 0.17 g/l, xenon about 5.49 g/l and, N₂ about 1.17 g/l and as such, these density variations allow the successful extraction of the hyperpolarized gas according to the present invention.

[0108] In one embodiment, as shown in FIG. 7, the hyperpolarized gas is ³He which is a relatively light gas (low density). As such, the extraction gas 670 is fed into the bottom of the container and the increasing volume of the extraction gas into the container 50C forces the lighter weight gas (³He) to exit the top of the container through the exit port 234 into a collection vessel 250 or delivery site. In contrast, as shown in FIG. 8, the hyperpolarized gas is ¹²⁹Xe, which is a relatively heavy gas (high density). As such, the extraction gas 770 is introduced into the top of the container and forces the heavy hyperpolarized gas out of the bottom through the exit port 234. In one embodiment, the extraction gas 670, 770 is introduced at a rate and in a way which allows it to contact the hyperpolarized gas at a front boundary plane but remain substantially independent of the hyperpolarized gas as the hyperpolarized gas is pushed/forced out of the container (i.e., the gases remain substantially unmixed). In another embodiment, the extraction gas 670, 770 is introduced to mix with the hyperpolarized gas to form a gas mixture—preferably by the time the gas reaches the exit port 234. The amount of hyperpolarized gas in the mixture is preferably such that the mixture provides a sufficient amount of the hyperpolarized gas for signal imaging (for useful MRI clinical images) and is suitable for patient inhalation. Preferably, for this embodiment, the container is configured and sized to provide at least one patient-inhalable dose of the hyperpolarized gas mixture. It is also preferred that the container be configured with the ports 230, 234 positioned on opposing sides or ends of the container and offset (side to side) relative to the other. As shown, the inlet and outlet ports 230, 234 are positioned on opposing sides of the centerline of the container and more preferably on opposing sides and ends (opposing quadrants) of a two-dimensional axis 200 drawn through the center thereof (see FIG. 7).

[0109] D. Mechanical Extraction

[0110] In this embodiment, mechanical extraction means such as pumps (diaphragm, rotary, or centrifugal pumps) or other devices are employed to act as a gas transfer source to pull or extract the hyperpolarized gas from the container in a manner which inhibits the depolarization of the hyperpolarized gas. If pumps or other active mechanisms are employed, the gas contact surfaces and components of the devices can be masked to inhibit direct contact with the hyperpolarized gas, as described above, and/or, alternatively, formed or coated from hyperpolarization-friendly materials.

[0111] 1. Syringe Extraction

[0112] Providing reliable dose quantities of hyperpolarized gas can be important to ensure that a patient receives an appropriate amount of hyperpolarized gas which will yield clinically useful data or which is in an amount or mixture approved by the applicable regulatory agency. Hyperpolarized gas can be characterized as having several primary “image related” variables such as: (1) the extent of polarization (i.e., what percent of the noble gas nuclei are hyperpolarized); (2) the volume of the hyperpolarized gas dispensed (such as inhaled or injected); and (3) the polarization life of the hyperpolarized gas (the polarized state of the gas will end, sooner or later, depending on several factors). The extent of polarization can be measured in a number of ways as is known to those of skill in the art, some of which are described in co-pending and co-assigned U.S. patent application Ser. Nos. 09/333,571 and 09/344,000, the contents of which are hereby incorporated by reference as if recited in full herein. See also published PCT Application Serial No. WO/9917105.

[0113] As regards dispensing hyperpolarized gas in the gaseous state, because gases by their very nature expand to fill the volume of the container they occupy, and are compressible to high pressures, measuring or meting the volume of a hyperpolarized gas in gas phase can be problematic. Nonetheless, measuring or meting the hyperpolarized gas in manner which can yield a predictable or substantially controlled quantity is desirable for proper dosing (and maybe, for commercial approval, may even be mandated by federal regulatory agencies). The present invention provides extraction and/or dispensing methods which can yield meted or measured and relatively reliable (preferably “precise”) quantitative doses of hyperpolarized gases and hyperpolarized gas mixtures.

[0114] In one embodiment, as shown in FIGS. 9A and 9B, a gas-tight syringe 870 is introduced into the container or transport vessel 50D such that it is in fluid communication with the hyperpolarized gas therein. The syringe 870 can connect to a container through an externally accessible port 810 that is configured to provide the gas-tight (and air-tight) seal. Suitable seal configurations include septum and luer-type connectors and/or other sealing means. As shown in FIG. 9A, the container 50D can include a valve 831 positioned intermediate the chamber 834 and the access port 810 for helping facilitate the integrity of the seal 810 during increased pressures sometimes experienced by the container during shipping and storage. In operation, the valve 831 is opened, one end of the syringe 871 is introduced into the access port of the container 810 and a controlled quantity of hyperpolarized gas is withdrawn into the chamber 872 of the syringe (pulled out) upon retraction of the plunger 873 therein. The hyperpolarized gas is then enclosed in the syringe 870 and can conveniently be discharged into the patient delivery unit (such as an inhalation mask) or into another delivery vessel such as a collapsible bag 250 as shown in FIG. 9B. Preferably, the syringe 870 is formed from a polymer or coated with a polymer or high purity metal coating on the gas contact surfaces to inhibit or minimize any depolarization attributed thereto. Also preferably, the syringe 870 is pre-conditioned to de-oxygenate the residual gas in the chamber 872 such as by evacuating and purging as described above. See also U.S. Pat. No. 6,128,918, the contents of which are incorporated herein by reference as stated above.

[0115] As illustrated by FIG. 9B, to deliver or discharge the hyperpolarized gas, the syringe 870 is preferably inserted into a port which is positioned in communication with the patient delivery vessel 250. The plunger of the syringe 873 is depressed and the gas is “pumped” out of the syringe and discharged into the patient delivery vessel 250. Similar to the access port 810 above, the delivery access port 885 preferably forms an airtight seal with the syringe 870 to introduce the hyperpolarized gas into the container/port 885 without contaminating the hyperpolarized gas sample with oxygen.

[0116] As shown by FIG. 9B, a coupling member 880 is configured to provide the sealed pathway to deliver the gas from the syringe 870 to the delivery container 250. The coupling member 880 provides the path connections 885, 888 to the syringe 870 and the patient delivery vessel 250 or inhalation mask (FIG. 13, 255) respectively. Although not shown, valves and other seal arrangements can also be employed as discussed above.

[0117] In another embodiment, as shown in FIG. 16, a gas-tight syringe 870 is used to extract a desired amount of hyperpolarized gas from a first container 50. In certain embodiments, the first container 50 is the optical or polarization cell held within the polarizer 10′ itself. The gas-tight syringe 870 is connected at the exit port 106 of the polarizer 10′ as shown in FIG. 16, the exit port 106 being in fluid communication with the polarization cell 50. However, the methods of the instant invention are not limited to the use of a polarization cell as the first container 50; they can also be used to dispense from other containers such as multi-dose transport or collection containers and the like.

[0118] As is illustrated in FIG. 16, the syringe 870 is configured such that it is in fluid communication with the first container 50 and also in fluid communication with a second vessel 250 via tubing 881, 892 (or other pathway means such as conduit or pipe). The system 800 can be configured to attach to each of the containers in sequence or concurrently via valve means and tubing and the like. The first container 50 is the vessel used to supply or fill the syringe 870 with hyperpolarized gas (or hyperpolarized gas mixtures) and the second vessel 250 is the vessel to which the syringe 870 metes the gas. The second vessel 250 can be sized and configured to hold a single patient dose or for multiple doses. In certain embodiments, the second vessel 250 is a single dose collapsible container. The second vessel 250 (and associated transfer of gas from the syringe 870 thereto) can be located at the production site or at a remote distribution site (or even at the end use site itself). The syringe 870 itself can be sized to hold from about 0.1 liters to about 5.0 liters of gas, and more typically sized from about 0.5-2.0 liters of gas. Of course, a plurality of various sized gas syringes can also be used spanning desired volumes, thereby allowing an operator to select the size appropriate for the particular application (thereby reducing the likelihood that undue quantities of hyperpolarized gas will be wasted from the meted transfer). A 1.5 liter gas syringe is available from the Hamilton Company of Reno, Nev. The O-ring/fitting on this conventional gas syringe, as well as the connections along the tubing of the extraction system 800, may be modified to improve the quality/integrity of the seals (decrease the leak rate through the seals). The quality of the seal can be improved by placing a sealant compatible with medical applications and which do not introduce undue decay of the hyperpolarized gas between the two components where a seal may be used. An example of a suitable sealant is an FDA or regulatory agency approved clear silicone. In the particular situation of the syringe 870, the quality of the seal can be improved by placing such a sealant between the port 870 p and the body of the syringe 870.

[0119] Generally described, in operation, after suitable preparation to remove contaminants from the flow path (such as the syringe 870 and the tubing 881, 892), hyperpolarized gas is directed out from the first container 50 into the syringe 870. The syringe plunger 873 translates away from the inlet/outlet port region of the syringe 870 p in response to gas directed therein. The syringe 870 can include graduations or visual indicia of volume 870 g which allows identification of the quantity received therein (and directed out therefrom when dispensing from same). When a sufficient supply of gas has been introduced into the syringe 870, the supply source is shut off via a valve means associated therewith (typically mounted on/integral with the polarizer unit 10′) to prevent additional gas from exiting the polarizer exit port 106.

[0120] To mete out a desired quantity, the second vessel 250 (suitably prepared to remove contaminants) is positioned to be in fluid communication with the syringe 870. The plunger 873 is advanced toward the inlet/outlet port end of the syringe 870 p to push the gas out of the syringe 870 into the tubing or conduit 892 toward the second container 250. When the plunger 873 has advanced to a desired graduation mark or visual indicia 870 g, an operator (or computer if the filling process is automated) halts the movement of the plunger 873 and closes valves 890, 891 or other shutoff means operably associated with the syringe 870 and the second container 250. As such, the receiving container 250 captures the meted quantity of gas. The second vessel 250 with the meted quantity of hyperpolarized gas can then be detached from the flow path. Thus, a meted quantity of gas is dispensed into the receiving container 250 allowing for predictable hyperpolarized doses.

[0121] As shown in FIG. 16, the supply source or container 50, the syringe 870, and the second vessel 250 form part of an extraction system 800. As is also shown, the extraction system 800 includes conduit or tubing 881, 892 as well as a plurality of valves 890, 891 and connectors 888 positioned therealong. Generally stated, the valves 890, 891 are configured to control the directional flow of the gas associated with the preparation (cleaning/purging), filling, and dispensing or meting of the gas into and out of the syringe 870 and secondary container 250.

[0122] In the embodiment shown, the syringe 870 and the second vessel 250 are each associated with valving means 890, 891, respectively, such that each can be individually isolated from the remainder of the extraction system 800. Suitable valving means include, but are not limited to, tubing clamps, hemostats, luer-type valves, stopcocks, and glass or aluminum (or formed or coated with other polarization friendly material) valves. Seals, threaded members, O-rings, connectors 888 and valving means 890, 891 should be attached to the tubing or flow path so as to provide sufficiently leak proof or air-tight seals to allow the system 800 to be able to maintain a vacuum of at least about 50 millitorr for a period of 1 hour at the time the dose is extracted or a vacuum sufficient to inhibit oxygen from entering the system in amounts which are unduly degrading to the hyperpolarized gas. The vacuum requirement can vary (such as a higher pressure) if increased cycles of purging and evacuating of the extraction system 800 is performed and depending on when and how quickly the dispensing is carried out relative to the purging evacuating methods. In certain embodiments, the system 800 can be sufficiently leak-tight so as to have a leak rate of less than about 5×10⁻⁵ cm³/s of helium at a pressure differential of about 1 atmosphere. EP O-rings AS568A-012 may be suitable to seal the syringe 870 to the tubing/connector. In certain embodiments, the system 800 may be configured such that the leak rate is less than about 0.3 cc's (cubic centimeters) per hour. This can allow a syringe 870 to have a “wait” time of about one hour.

[0123] The second vessel 250 can be configured such that it can be detached (with its associated valve 891) via a gas-tight connector 888 from the remainder of the extraction system 800. Acceptable connectors include, but are not limited to, luer type connectors, Chemthread™ connectors, and compression fittings.

[0124] Additionally, as noted above, when the polarization cell 50 is used as the polarized gas source, the secondary vessel 250 is placed in fluid connection with both the syringe 870 and the first vessel 50. Valves 890, 891 can isolate the syringe 870 and the second vessel 250. Prior to filling the syringe 870 with a gas, a vacuum can be used to check for leaks in the connections of the extraction system 800. In addition, the syringe 870, secondary vessel 250, and connecting tubing 881, 892 are pre-conditioned such as by purge/evacuation methods to clean out residual deleterious elements within, such as oxygen.

[0125] The syringe 870 is connected to the first vessel 50 via a connector 106 and tubing 881 (such as Tygon® or PFA Swagelok tubing). The tubing 881 can be sized with a small inner diameter gas flow passage (less than about ¼ inch) to reduce the volume of gas held therein (this allows the volume of gas trapped therein after the gas is meted from the syringe to be disregarded as it contains a negligible quantity) while also being sufficiently large to allow free flow of the gas and to evacuate same (typically to levels of about 50 millitorr). Of course, the extraction system 800 can be sized and configured with a known volume to dispense a quantity larger than the amount which will be meted into the second vessel 250. The dead volume quantity can be predetermined and can be added to the quantity of gas remaining in the syringe. The two volumes can be added together and subtracted from the quantity of gas initially held in the syringe thereby providing a reliable accounting of the quantity of gas dispensed. In addition, the syringe can include a set of correction graduation marks adjusting the volume to offset the dead volume thus visually identifying by graduation marks disposed on the syringe body itself. For example, for a quantitative conventional graduation mark that indicates that 1.1 liters of gas has been transmitted from the syringe, and for a dead volume of about 0.10 liters, an alternative graduation mark can be disposed on the syringe to read 1.0 on the corrected graduation to reflect the quantity that is dispensed into the receiving container.

[0126] The gas-contacting surfaces of the syringe 870 can include substantially non-depolarizing materials such as aluminum, titanium, or a substantially non-depolarizing plastic. In certain embodiments, the gas-contacting surfaces of the syringe 870 are comprised of non-depolarizing plastics such as one or more of polyolefins, polymethylmethacrylate, polycarbonate, polystyrene, polymethacrylate, polyvinyl, polydiene, polyester, polyamide, polyimide, polynitriles, cellulose and cellulose derivatives and blends and mixtures thereof. The syringe 870 can be further lubricated (to enhance the movement of the plunger 873) with a non-toxic, substantially non-depolarizing vacuum grease such as one or more of a hydrocarbon grease (such as Apiezon N) and/or an inert chlorofluorocarbon grease (such as Halocarbon 25-5S).

[0127] In another embodiment, the meted quantity of hyperpolarized gas may be mixed with a meted and/or predictable or controlled (preferably, substantially precise) amount of a buffer gas. Adding a buffer gas can advantageously decrease the rate at which the hyperpolarized gas atoms collide with each other, thereby decreasing the rate of depolarization. Additionally, it may be advantageous to be able to vary the volume of hyperpolarized gas to accommodate different polarization levels in order to obtain the same dose. Suitable buffer gases are those which can be administered in vivo to a subject (pharmaceutical grade/quality) and preferably include, but are not limited to, one or more of high purity/substantially pure (Grade 5 or better) helium, nitrogen, and argon.

[0128] As shown in FIG. 16, the extraction system 800 can be configured such that a single syringe 870 is used to dispense both the hyperpolarized gas and the buffer gas. In this embodiment, the buffer gas and hyperpolarized gas are sequentially metered out into the syringe 870 from the first container 50 (shown as the polarizer 10′) or the source of buffer gas (such as a pressurized cylinder) via the outlet port 106. The syringe 870 and tubing 881, 892 can be evacuated before the second gas is added to increase the reliability/accuracy of the resulting gas mixture. Therefore, a valve 891 on the secondary container 250 is used for single syringe 870 dispensing if a buffer gas is used. The buffer gas can be meted into the syringe 870 first because it does not have a decay time associated with it.

[0129] If a buffer gas is used, at least (and preferably more than) the ultimately desired amount of buffer gas can be dispensed into the syringe 870 with the valve 891 for the secondary container 250 closed and the secondary container 250 pre-conditioned and evacuated. The valve 891 for the secondary container 250 is then opened and the desired amount of buffer gas is forced into the secondary container 250 by depressing the plunger 873. The valve 891 for the secondary container 250 is closed again, and the tubing 881, 892 and syringe 870 are evacuated again. The hyperpolarized gas is then dispensed into the syringe 870, in an amount equal to or exceeding the amount of hyperpolarized gas desired for dispensing into the second container 250. As above, after the valve to the secondary container 891 is opened, the desired amount of hyperpolarized gas is forced into the secondary container 250 by depressing the plunger 873 on the syringe 870. The valve 891 on the secondary container 250 is closed again, and the secondary container 250 is removed from the extraction system 800 via its connector 888.

[0130] Referring now to FIGS. 20A and 20B, another embodiment of a meted dispensing system 800 using a syringe 870 is illustrated. This embodiment may be particularly suitable for meting small amounts of hyperpolarized gas (smaller than about 20 ml-50 ml) although other amounts of gas can also be meted using the methods and devices of embodiments of the present invention. That is, a single syringe 870 can be used to hold, measure, and mix the amount of and dilution of the hyperpolarized gas. The non-polarized gas is introduced into the syringe first in a desired quantity, the quantity can represent the desired portion of the ultimate dose or mix amount. Introducing the non-polarized gas into the syringe 870 initially and holding the gas therein while directing the hyperpolarized gas therein can have the benefits noted above and can also help decrease the surface to volume ratio of the chamber of the syringe and decrease the depolarizing effect of the container walls on the polarized gas. The polarized gas (or a polarized gas mixture) is then dispensed into the same syringe 870 while the non-polarized gas is held therein. The additional volume increase (even if gradual or small) can be measured as the plunger is pushed a further distance away from the port 810 in response to the amount of gas directed therein and the gas mixture can be dispensed from the syringe into the second container 250. The proportion of the non-polarized gas to the polarized gas is known (allowing a determination as to the apparent polarization of the gas mixture) as is the total volume. This information allows for identification of the polarization strength and dose volume of the hyperpolarized gas mixture dispensed and held in the second container 250.

[0131] In operation, after the lines/system is prepared (evacuation/purge to remove contaminants/oxygen, and the like), as shown in FIG. 21A, a desired amount of suitable non-polarized gas such as a buffer gas or gases (described above which include, but are not limited to, one or more of high purity/substantially pure (Grade 5 or better) helium, nitrogen, and argon) is directed into the syringe 870 through a gas port 870 p so that the end of the plunger 873 moves away from the body of the syringe in a direction away from the gas port 870 p (shown by the direction of the arrow head) in the chamber of the syringe. Next, as shown in FIG. 21B, while the non-polarized gas is held in the syringe 870, a desired amount of gaseous hyperpolarized noble gas is introduced into the syringe, forcing the plunger to travel a greater distance away from the gas port 870 p. In this way, even relatively small amounts of hyperpolarized gas can be measured as the movement is detected relative to the non-polarized gas already present in the chamber. In certain embodiments, additional amounts of non-polarized gas (the same or different from that already in the chamber) may be added to the mix as desired (not shown). In any event, the plunger is then depressed and the polarized gas mixture is directed out of the syringe 870 into the delivery path and the desired container 250. The step of pre-filling the syringe with a quantity of the non-polarized gas can be performed prior to and proximate in time with the introduction of the polarized gas, or at a point in time in advance of the filling of the hyperpolarized gas. See co-assigned U.S. patent application Ser. No. 09/334,400 for a discussion of preparing collapsible containers for receiving hyperpolarized gas; the contents of this document are hereby incorporated by reference as if recited in full herein.

[0132] In certain embodiments, the evacuation/purging preparation methods can be carried out and then the extraction system (or portions of the extraction system such as the syringe) can be filled with a high-purity inert purge gas until the pressure is at or slightly above atmospheric pressure. The inert purge gas will either not leak from the extraction system (or components thereof) or leak out of the extraction system during periods of non-use (while the extraction system is waiting to initiate the dispensing operations). This will inhibit oxygen from leaking into the extraction system and can reduce the amount of depolarizing oxygen that may come into contact with the hyperpolarized gas. This, in turn, can allow the time between the evacuation and purges to be extended (relative to the dispensing procedures). The purge gas can be introduced in a manner that compensates for the dead volumes in the flow path. The purge gas can then be evacuated prior to the active dispensing or can form part of the dose mixture.

[0133] In certain embodiments, nitrogen gas is dispensed into the syringe 870 in an amount between about 20 ml-1.5L, and hyperpolarized gas (³He or ¹²⁹Xe or a mixture thereof) is introduced into the syringe thereafter in an amount between about 10 ml-1.4 liters or more, such that the gases are held together in the chamber to form the desired dose mixture typically in the range of about at least 10% hyperpolarized gas with final volume doses generally in the 100 ml to 1500 ml or 2 liter range. In certain embodiments, about 10-90% of the gas in the gas mixture is hyperpolarized gas. Preferably about 20-75% of the gas in the gas mixture is hyperpolarized gas.

[0134] In particular embodiments directed to hyperpolarized ³He, about 350 cc's of hyperpolarized ³He polarized to at least about 40% can be diluted with about 650 cc's of N₂. In other embodiments, about 100 cc's of hyperpolarized ³He can be diluted into about 400-900 cc's of N₂. For particular embodiments directed to hyperpolarized ¹²⁹Xe, about 500-1000 cc's of hyperpolarized ¹²⁹Xe can form the administration dose for the subject such that the dose employs no, or relatively small amounts (less than about 1-10%), of carrier gas.

[0135] A dual syringe alternative embodiment is shown in FIGS. 17A and 17B. In this embodiment, a second syringe 870′ can be used to dispense the buffer gas separate from the syringe 870 used to dispense the hyperpolarized gas. In this embodiment, the buffer gas is directed into and held in the second syringe 870′ and subsequently meted into a patient delivery vessel or other container 250. Preferably, the buffer gas is dispensed into the buffer gas syringe 870′ prior to the introduction of the hyperpolarized gas into its syringe 870 to reduce depolarization of the hyperpolarized gas as it waits to be directed into the second container 250.

[0136] In operation, when the two syringe system is used, the buffer gas is dispensed into its syringe 870′, as before, while both the secondary container 250 and the hyperpolarized gas syringe 870 are closed by their associated valves (891 and 890 respectively). The valve 891 on the secondary container 250 is opened and the desired amount of buffer gas is forced into the secondary container 250. The valves of the secondary container and buffer gas syringe 891 and 890′, respectively, are closed again while the tubing 881, 892, 892′ (the ‘dead volume’) is evacuated. The valve 891 associated with the hyperpolarized gas syringe 870 is then opened and an appropriate amount of hyperpolarized gas is directed therein. The valve associated with the hyperpolarized gas syringe remains open. Next, the valve 891 on the secondary container 250 is opened and the desired amount of hyperpolarized gas is dispensed from the syringe 870 to the secondary container 250. Finally, the valves on the hyperpolarized gas syringe and secondary container 890, 891 (with the valve for the buffer gas syringe remaining closed) are closed which then allows the secondary container 250 to be removed from the extraction system 800 via the connector 888 without disrupting the remainder of the extraction system 800 or contaminating any residual hyperpolarized gas in the hyperpolarized gas syringe 870. Another secondary container 250 can then be attached to the system and the process can be repeated.

[0137] Alternatively, the hyperpolarized gas can first be directed into the second container 250 with the buffer gas subsequently directed therein. For example, a quantity of buffer gas such as nitrogen can be dispensed into the buffer gas syringe 870′. The dead volume associated with the gas flow paths 881, 892, 892′ is then evacuated. A desired amount of the hyperpolarized gas is then directed into the hyperpolarized gas syringe 870. The syringes are isolated from the remainder of the system and the dead volume (and second container 250 if desired) is evacuated. A desired amount of hyperpolarized gas is meted out of the hyperpolarized gas syringe 870 and then the buffer gas is used to push the hyperpolarized gas into the second container 250 out of the dead volume 881, 892, 892′ and to top off the gas mixture with a desired volume of the buffer gas. Thus, in this embodiment, the buffer gas can push the hyperpolarized gas from the tubing into the second container 250. In an additional alternative embodiment, a first quantity of buffer gas can be first directed into the second container 250, then the hyperpolarized gas can be directed therein, and finally, a second quantity of the same or a different buffer gas can be directed into the second container 250. Preferably, for a 0.5-2 liter quantity of buffer gas and hyperpolarized gas mixture, about 10-90% of the gas mixture is hyperpolarized gas, and more preferably about 20-75% of the gas in the mixture is hyperpolarized gas.

[0138] It is also noted that a pre-filled buffer gas syringe can be employed with the meting system according to the present invention. That is, because no polarization decay is associated therewith, the buffer gas syringe can be conveniently pre-filled in advance of the polarization of the gas, stored for use, and then connected to the gas extraction system at the appropriate time such as proximate the meting operation. In addition, the second container 250 can include two sealable ports and the gas flow path can be connected such that the hyperpolarized gas has a first flow path extending from the first syringe 870 into the container 250 and the buffer gas has a second flow path extending from the second syringe 870′ to the container 250 such that the second flow path is different from the first flow path (not shown); this configuration which can allow concurrent meting of buffer gas and hyperpolarized gas therein.

[0139] Advantageously, this dual syringe system decreases the likelihood that the relatively expensive hyperpolarized gas will be unduly wasted. For example, since the syringe 870 is not required to be evacuated after the extraction procedure commences, if an excess of hyperpolarized gas is dispensed into the syringe 870 accidentally, that hyperpolarized gas is not wasted and can be used to fill a subsequent secondary container 250.

[0140]FIG. 17B illustrates that the two syringes 870, 870′ can be held side by side in a holding apparatus for convenient interconnection to the first container 50 (preferably via the exit port on the polarizer 10′). If the buffer gas syringe 870′ is held in close proximity to the hyperpolarized gas syringe 870, then preferably it is formed of substantially non-depolarizing materials to reduce the likelihood that is presence will promote polarization decay. As is shown, the holding apparatus 801 includes a first platform 801 a and a second opposing platform 801 b sized and configured to hold the syringes 870, 870′ in substantial side by side alignment therebetween. A plurality of ribs 801 r can be used to interconnect and provide the desired rigidity to the holding apparatus. Preferably, the ribs and platforms 801 r, 801 a, 801 b are configured to hold the syringes 870, 870′ recessed a distance into the body of the apparatus 801 to reduce the likelihood that the syringes will be hit by inadvertent contact during operation. In any event, it is preferred that the holding apparatus 801 be configured such that the graduations/visual indicia 870 g, 870 g′ are visible during use.

[0141] The first platform 801 a includes two apertures 801 o sized to allow the plunger rod 873 e to extend and translate therefrom. The second platform 801 b includes apertures (not shown) for the inlet/outlet port 870 p, 870 p′ to allow the gas to flow to the desired syringe therein. Of course, other holding apparatus configurations can also be used. As a non-limiting example, two separate holding apparatus (one for each of the syringes) which can be joined together or held in a desired position on a cart or other structure (stationary or not as shown in FIG. 16) to help maintain secure air tight connections during operation (and preferably connected to reduce the length of the conduit used to mete the gas(es)). As shown in FIG. 16, a similar holding apparatus can be used for a single syringe system.

[0142] In another preferred embodiment as shown in FIG. 18, a plurality of secondary containers 250A-250E can be filled sequentially with an extraction system 800 according to the present invention. As shown in FIG. 18, a plurality of secondary containers 250A-250E can be connected via gas-tight individually detachable connectors 888A-888E from the extraction system 800. Thus, similar to the embodiment described above, each of the plurality of secondary containers 250A-250E is associated with a valve 891A-891E with which it is in fluid communication. The valves 891A-891E advantageously allow the secondary containers 250A-250E to be pre-processed (as described hereinabove) and filled independently of the others. Therefore, the plurality of secondary containers 250A-250E can be filled sequentially, and can be filled utilizing one (not shown) or two syringes (870, 870′). As before, it is more preferable that a substantial quantity of the buffer gas, if used, be dispensed into each secondary container 250A-250E before the hyperpolarized gas is extracted from the primary container 50. Of course, the filling of a plurality of second containers 250A-250E can also be carried out simultaneously.

[0143] Preferably, particularly for longer dispensing time periods (i.e., longer than about five to ten minutes), a magnetic field generator means is positioned proximate the hyperpolarized gas to enclose the hyperpolarized gas syringe 870 with a magnetic field as shown in FIG. 19. In one embodiment, the magnetic field generator means can be mounted onto the cart shown in FIG. 15. The magnetic field generator means can either comprise permanent magnets (not shown) or electromagnets 820A, 820B, as long as the field strength is sufficient to shift the resonant frequency of the gas above the region of ambient noise and minimize the effect of ambient gradients on the gas. A more complete discussion of magnetic holding fields can be found in co-assigned U.S. Pat. No. 6,269,648, the contents of which were incorporated by reference hereinabove. It is also preferred that if a magnetic field generator is used, a means for assessing the extend of polarization in the gas is also used. For example, an NMR excitation coil can be positioned proximate the hyperpolarized gas syringe 870 or in the flow path or even adjacent the first or second container (or even at multiple of these or other locations within the extraction system).

EXAMPLE

[0144] A suitable precision fluid measuring product gas tight syringe is available from the Hamilton Company located in Reno, Nev. This syringe can be modified by changing the fitting 870 p and the plunger 873. That is, the magnetic metal fitting conventionally used on this syringe where the line connects to the body of the plunger was replaced with a plastic (polypropylene) fitting and the plunger was replaced with a plunger formed of polyethylene plastic.

[0145] T₁ measurements were taken for the syringes holding only or (substantially pure or about 100%) ³He. For about a one liter quantity of ³He gas in the syringe held within a protective magnetic holding field of about 7 Gauss a T₁ of about 3 hours was measured. For about 950 cc's (a similar quantity) of the substantially pure ³He not held in a protective holding field a T₁ from about 10-17 minutes was obtained.

[0146] Additionally T₁ measurements were taken for gas mixtures meted according to the present invention into a disposable patient collapsible bag holding a one liter mixture of hyperpolarized ³He gas with about a 50% concentration of the polarized gas and about a 50% blend of N₂ buffer gas, using the single syringe meting method discussed above, the T₁ for the bag was measured at about 11.4 hours. In comparison, when the hyperpolarized ³He gas was dispensed directly into the bag from the polarizer, the measured T₁ was about 12 hours. Thus, the meting method of the present invention resulted in only a very minor loss of O₂ as evidenced by the slight decrease in T₁.

[0147] Advantageously, these methods allow controlled amounts of the gas to be introduced into the delivery device/vessel, thereby allowing more precise and/or reliable amounts of hyperpolarized gases and gas mixtures to be transported, which in turn can reduce residual waste caused by unused gas left in the container as well as provide for more repeatable dose quantities. Further, controlled delivery and extraction allows a more predictable delivery dosage and potentially decreases product costs (particularly for commercial sized production runs and/or use) over that of typical conventional systems.

[0148] 2. Inflatable Extraction

[0149]FIGS. 10 and 11 illustrate another embodiment of the present invention. The container 50E includes a resilient member 910 positioned in the container 50E such that it is in fluid communication with the hyperpolarized gas in the container. In operation, the resilient member 910 expands from a first position (shown in FIG. 10) to a second position (shown in FIG. 11). Thus, the expanded resilient member 910 translates a further distance or depth into the container to expel the hyperpolarized gas out of the exit port 936 into the delivery path or patient delivery vessel 250. The expansion is responsive to fluid introduced into the fluid entry port upstream of the container. As shown, the resilient member 910 is positioned intermediate the fluid entry port 915 and the hyperpolarized gas in the container 50E. The exit port/path 934 of the container 50E is preferably positioned opposing the inlet port 915 as described for the liquid extraction method above. As shown in FIG. 11, the collapsed resilient member 910 extends a small

[0150] Preferably, the resilient member 910 is securely attached to the container such that it forms a fluid-tight seal around the walls or circumference of the inlet port 915. A valve 916 can be positioned upstream of the resilient member to minimize oxygen entry into the container. As shown in FIG. 11, this sealed attachment will permit the resilient member to act as a barrier surface 925 to contain the fluid(s) introduced to expand the resilient member 910 separate and apart from the hyperpolarized gas. Alternatively, the resilient member 910 can be configured to expand with fluid introduced therein, while also letting a portion of the expansion fluid enter the container 50E downstream of the resilient member 910 to form a gas mixture as was described for the gas extraction method above. For example, an expansion gas comprising nitrogen can be introduced into the fluid entry port 915 and used to inflate the resilient member 910. The resilient member 910 can include apertures or be secured to the container in a way to define apertures to allow a portion of the nitrogen to pass therethrough (not shown). The nitrogen and hyperpolarized gas are then pushed out of the exit port 934 by the inflated positions of the resilient member 910.

[0151] In any event, as the resilient member barrier surface 925 contacts the hyperpolarized gas, it is preferred that it be formed from a polarization-friendly material (or coated with same) so as to inhibit contact induced polarization attributed thereto.

[0152] Once the hyperpolarized gas has been extracted from the transport vessel it can be captured in a patient delivery system such as a collapsible bag 250 as shown in FIG. 11. The bag can be conveniently compressed to force the hyperpolarized gas into an inhalation mask 255 positioned on a subject. Alternatively, the hyperpolarized gas can be extracted as described herein, but delivered directly to the subject as illustrated in FIG. 13.

[0153] E. High Efficiency Transport Vessel

[0154] In one embodiment, which can reduce the need for an active or mechanical secondary means of extraction, the container itself can be alternatively configured to reduce the amount of gas remaining in the vessel over conventional vessels. In this embodiment, a low volume, high pressure transport vessel is configured to transport hyperpolarized gas. Even without a secondary means of mechanical extraction, the gas in the container can be released to stabilize with atmospheric pressure as described for conventional extraction methods. However, because containers with smaller chambers are used, a lesser volume of gas remains in the chamber at the 1 atm condition compared to larger low-pressure transport vessels.

[0155] In certain embodiments, the container is sized and configured to be 500 cc's (cubic centimeters) or smaller, and pressurized to about 3-10 atm of pressure. For ³He, the container can be sized to be less than about 200 cc's and pressurized at about 5-10 atm. In certain embodiments, the ³He container is sized at about 200 milliliters or less, and pressurized to about 6-10 atm. This will allow an equivalent gas content of about 1.2 liters, which allows a full one-liter to be extracted just by opening the valve to equalize to ambient pressure at the desired delivery point.

[0156] In another embodiment, the transport container 22 according to the present invention can be configured to act as the polarization chamber (FIG. 1, 22). In this embodiment, the transport container is the polarization chamber 22 and is detachable from the hyperpolarizer 10 (not shown). Thus, the transport container can be configured as a dual purpose vessel to allow polarization and still be configured to be a transport container as described hereinabove; this configuration can reduce the number of gas transfers, thereby improving the transfer efficiency and reducing the amount of residual gas that is wasted.

[0157] F. Cryo-Cooled Gas Extraction

[0158]FIG. 14 illustrates yet another aspect of the present invention. This figure illustrates one embodiment of an improved transfer method according to the present invention. More particularly, this figure shows cooling the container 50A to a desired temperature (preferably below the freezing point of water, i.e., sub-zero temperatures). More preferably, the container is cooled to at least about 195° K. (such as by exposing the container to a dry ice (CO₂). Most preferably, the cooling is carried out by exposing the container or chamber to cryogenic temperatures, such as to liquid nitrogen or liquid helium temperatures. For example, as shown in FIG. 14, the cooling is performed by exposing the container 50A to a liquid nitrogen bath (77° K.) 140. In this figure, a dewar 141 is configured to hold a quantity of cooling liquid and the container 50A is at least partially immersed therein. Although illustrated as immersed, the invention is not limited to thereto. The dewar 141 can be alternately configured to receive only a portion of the container therein, or to have a smaller amount of cooling liquid therein. In addition, of course, other cooling means can be used which are known to those of skill in the art including but not limited to refrigeration systems, ice baths, other cryogenic exposure techniques and the like, to cool the container to a desired temperature. In operation, the hyperpolarized gas exits the polarizer cell 22 and enters the cooled transport container chamber. The cooled walls of the container allow increased volumes of hyperpolarized gas in the chamber (compared to non-cooled chambers) thereby increasing the quantity of hyperpolarized gas captured therein. Stated differently, at lower temperatures, gas compresses according to the equation PV=nRT, therefore more gas can be contained in a chamber having a lower pressure.

[0159] Generally stated, the gas “packing effect” can be described by the ratio of room temperature to the coolant temperature. For liquid nitrogen, the packing effect can be expressed as 295/77 or 3.8. Thus, the packing effect for dry ice is about 295/195 or 1.51, while the value for the freezing point of water is only about 295/273 or 1.08. Thus, it is preferred that the coolant temperature be selected to provide a packing effect which is at least about 1.08, more preferably at least about 1.51 and most preferably at least about 3.8, although other values can be used. Of course, as noted above, preparing the container such as by evacuating and purging (to clean it before use) is important.

[0160] In one preferred embodiment, hyperpolarized ³He is collected in the cooled container or chamber. In another preferred embodiment, either ³He or ¹²⁹Xe exits the polarizer cell 22 and is directed into a closed container 50A such that the hyperpolarized gas mixture (with the alkali metals removed) which exits the polarizer cell (e.g., the “exhaust” mixture) is captured and enclosed by the container. The container can then be sealed and allowed to warm to ambient temperature. This is unlike the cryogenic cold finger apparatus used to continuously process ¹²⁹Xe (by retaining only the ¹²⁹Xe and directing the remainder of the gas mixture out of the container). In addition, tubing and other chambers positioned after the polarizer cell 22 or transferor vessel can also be cooled.

[0161] In another aspect of a preferred embodiment, the cryo-cooled gas extraction is carried out under temperature control to provide a more “controlled” or exact filling amount of gas to be directed into the container. One way to control temperature during the cryo-cooling process is to direct cold nitrogen gas to flow across a heater element positioned proximate to the transport container. A temperature sensor can be positioned adjacent the transport container to measure temperature of the container. This information feeds back to the heater element to automatically turn it “off” or “on” so as to maintain the desired temperature of the transport vessel (between room temperature and the coolant temperature). This would allow variable temperature (from about 77 K. to room temperature) across the transport container. This controlled temperature gradient can allow consecutive transfer or receiving vessels to be filled with (substantially) the same amount of hyperpolarized gas. This controlled amount is desired (within certain tolerance ranges) so that a precise dosage can be delivered or administered to a patient. For example, upon extraction of gas into a first container, the polarizer cell starts with a pressure of about 8 atm. However, before the next consecutive container is filled, the cell pressure could be depleted. Thus, one could control the rate of extraction via temperature gradients to control the amount of gas which exits the cell into the temperature controlled (temperature gradient) container to deliver a substantially equal amount to the two consecutively filled containers. Alternatively, multiple containers (not shown) can be plumbed to be filled simultaneously such as by concurrently engaging two or three or more (preferably similarly sized) containers with the polarization cell such that each is cooled to the same temperature. The hyperpolarized gas flow could be directed down an main exit channel and split into channels equidistant from the cell. Preferably the multiple containers have the same size, volume, and (cooled) temperature. The split channels direct the gas into the containers in communication therewith to obtain substantially the same amount of gas in each container.

[0162] G. Container/Materials

[0163] Because the shape of the container area can impact the rate of depolarization, it is preferred that container configurations be selected to maximize the free-gas volume of the container (V) while minimizing the surface area (A) which contacts the hyperpolarized gas (that is, to decrease the value of the ratio A/V). More preferably, the container is sized and configured to provide a A/V ratio of about less than 1.0, and even more preferably less than about 0.75. In one embodiment, the container is substantially spherical.

[0164] Preferred container materials include non-magnetic high-purity metal films, high-purity metal oxides, high purity insulators or semi-conductors (such as high purity silicon) and polymers. As used herein, “high purity” includes materials which have less than about 1 ppm ferrous or paramagnetic impurities and more preferably less than about 1 ppb ferrous or paramagnetic impurities. Preferred polymers for use in the containers described herein include materials which have a reduced solubility for the hyperpolarized gas. For the purposes of the inventions herein, the term “polymer” to be broadly construed to include homopolymers, copolymers, terpolymers and the like. Similarly, the terms “blends and mixtures thereof” include both immiscible and miscible blends and mixtures. Examples of suitable materials include, but are not limited to, polyolefins (e.g., polyethylenes, polypropylenes), polystyrenes, polymethacrylates, polyvinyls, polydienes, polyesters, polycarbonates, polyamides, polyimides, polynitriles, cellulose, cellulose derivatives and blends and mixtures thereof. It is more preferred that the coating or surface of the container comprise a high-density polyethylene, polypropylene of about 50% crystallinity, polyvinylchloride, polyvinylflouride, polyamide, polyimide, or cellulose and blends and mixtures thereof.

[0165] Of course, the polymers can be modified. For example, using halogen as a substituent or putting the polymer in deuterated (or partially deuterated) form (replacement of hydrogen protons with deuterons) can reduce the relaxation rate. Methods of deuterating polymers are known in the art. For example, the deuteration of hydrocarbon polymers is described in U.S. Pat. Nos. 3,657,363, 3,966,781, and 4,914,160, the disclosures of which are hereby incorporated by reference herein. Typically, these methods use catalytic substitution of deuterons for protons. Preferred deuterated hydrocarbon polymers and copolymers include deuterated paraffins, polyolefins, and the like. Such polymers and copolymers and the like may also be cross-linked according to known methods.

[0166] It is further preferred that the polymer be substantially free of paramagnetic contaminants or impurities such as color centers, free electrons, colorants, other degrading fillers and the like. Any plasticizers or fillers used should be chosen to minimize magnetic impurities contacting or positioned proximate to the hyperpolarized noble gas.

[0167] Alternately, in another embodiment, the contact surface can be formed from a high purity metal. The high purity metal can provide advantageously low relaxivity/depolarization resistant surfaces relative to hyperpolarized noble gases.

[0168] As noted above, any of these materials can be provided as a surface coating on an underlying substrate or formed as a material layer to define a friendly contact surface. If used as a coating, the coating can be applied by any number of techniques as will be appreciated by those of skill in the art (e.g., by solution coating, chemical vapor deposition, fusion bonding, powder sintering and the like). Hydrocarbon grease can also be used as a coating. The storage vessel or container can be rigid or resilient. Rigid containers can be formed of Pyrex™ glass, aluminum, plastic, PVC or the like. Resilient vessels are preferably formed as collapsible bags, preferably collapsible polymer or metal film bags. Examples of materials which can provide oxygen resistance as well as low-solubility include but are not limited to PET (polyethylene terphthalate), PVDC (polyvinylidene dichloride), Tedlar™ (polyvinylfluoride), cellophane and polyacrylonitrile.

[0169] Preferably, care is taken to insure all fittings, seals, and the like which contact the hyperpolarized gas or which are located relatively near thereto are manufactured from materials which are friendly to polarization or which do not substantially degrade the polarized state of the hyperpolarized gas. For example, many commercially available seals are made from fluoropolymers which (with the exception of Tedlar™ noted above) are not particularly good for the preservation of either ¹²⁹Xe or ³He hyperpolarized gases because of the solubility of the hyperpolarized gas in the material.

[0170] Inasmuch as most common gasket materials are fluoropolymers, they can potentially have a substantially depolarizing effect on the gas. This effect, which can be particularly acute for ³He, can be attributed to a relatively high solubility of helium in most fluoropolymers due to the larger void space in the polymer attributable to the large fluorine atoms. It is preferred that the containers of the present invention employ seals, O-rings, gaskets and the like with substantially pure (substantially without magnetic impurities) hydrocarbon materials such as those containing polyolefins (including but not limited to polyethylene, polypropylene, copolymers and blends thereof). Additionally, hydrocarbon grease can be used to further facilitate or produce a vacuum tight seal. Thus, if a valve is used to contain the gas in the chamber 30, it is preferably configured with a magnetically pure (at least the surface) O-ring and/or with hydrocarbon grease. Of course, where fillers and plasticizers are employed, then it is preferred that they be selected to minimize the magnetic impurities such as substantially pure carbon black.

[0171] In an alternative embodiment, the O-ring seal can be configured with the exposed surface coated with a high purity metal as discussed for the container surface.

[0172] Similarly, the O-ring or seal can be coated or formed from an outer exposed layer of a polymer at least “L_(p)” thick. the inner layer thickness (“L_(th)”) is at least as thick as the polarization decay length scale (“L_(p)”) which can be determined by the equation:

L_(p)={square root}{square root over (T_(p)D_(P))}

[0173] where T_(p) is the noble gas nuclear spin relaxation time in the polymer and D_(p) is the noble gas diffusion coefficient in the polymer.

[0174] For example, a layer of substantially pure polyethylene can be positioned over a commercially available O-ring. One preferred O-ring material for ¹²⁹Xe is a Teflon™ coated rubber.

[0175] When bags with long surface relaxation times are used, other relaxation mechanisms can become important. One of the most important additional relaxation mechanisms is due to collisions of the noble gas with paramagnetic oxygen. Because O₂ has a magnetic moment, it can relax hyperpolarized gases in the same manner as protons. Given this problem, care should be taken to reduce the oxygen content in the storage container through careful preconditioning of the container, such as by repeated evacuation and pure gas purging procedures. Preferably, the container is processed such that the O₂ concentration yields a T₁ of about 1000 hours or more. More preferably, the container is processed to obtain an O₂ concentration on the order of about 6.3×10⁻⁶ atm or less or about 10⁻⁷ atm or less, and even more preferably less than about 1×10⁻¹⁰ atm. Additionally, as discussed above, the evacuation/purge procedures can include heating the container or other evacuating or pumping methods to additionally facilitate the removal of any remaining (monolayer) residual amounts of moisture or water.

[0176] Preferably, the patient interface and storage chambers and associated apparatus and tubing are prepared in advance of use to minimize any preparation required at the hospital or extraction site. Therefore, preferred pre-conditioning or equipment preparation methods such as cleaning, evacuating, and purging the connectable tubing and patient delivery vessel (see FIG. 3, 250, 251) or other components to remove oxygen and paramagnetic contaminants are preferably done off-site. After preparation/conditioning, the tubing 251 and delivery bag 250 can be stored at the hospital for use under pressure with a noble gas or benign liquid therein. This pre-filled gas or fluid storage can minimize the potential for the containers or components to de-gas (gas from the matrix of a material such as oxygen can migrate into the chamber onto the contact surfaces), and can also minimize air leaking into the container. Alternatively, or in addition to the pre-conditioning, the pressurized tubing and delivery vessels (and/or syringes) can be sealed with check valves or other valved ports. In another alternative, vacuum tight valves can allow the tubes and containers to be stored for use under vacuum rather than under positive pressure.

[0177] H. Calibration Station

[0178] Prior to introduction and/or delivery to a patient, the hyperpolarized gas can be calibrated for identification of the efficacy or polarization strength of the gas. This calibration will allow a “shelf-life” to be affixed to the delivery container alerting personnel as to the temporally limited useful life of the product. This positive identification can reduce the delivery of non-effective hyperpolarized gas to the patient. In certain embodiments, the calibration can be performed on the hyperpolarized gas at the end use site. The calibration can be performed on the gas subsequent to when it has been extracted from the shipping or transport container 50A-E. Typically, the hyperpolarized gas is calibrated when the gas is captured in the delivery vessel 250. The gas can be calibrated when it is positioned in a protected area (i.e., stable magnetic field) proximate to the end use site at the clinic or hospital facility. This allows a reliable representative calibration to be established on the product when it is in its final delivery container, or at its destination site, and/or when it is in a protected environment (such as proper shielding and/or homogenous magnetic fields) and is protected from potentially degrading elements (i.e., EMI, etc.) especially problematic during shipping. Also preferably, after calibration the container is configured with an external indicia of validation/inspection corresponding to an inspection date and a use-by date and or time.

[0179] In certain embodiments, the transport container is sized and configured to ship multiple dosages of the hyperpolarized gas, and then extracted at a protected destination site to form single dose patient delivery vessels. See, e.g., U.S. Pat. No. 6,269,648, the contents of which are hereby incorporated by reference as if recited in full herein. The single dose vessels can be tested for efficacy and externally dated/stamped or otherwise encoded with a preferred use date/time. This calibrated and externally visually identified product will allow operators to conveniently identify and remove “old” or “depolarized” product in advance of the patient delivery/end use.

[0180] Generally described, as shown in FIG. 15, the calibration is carried out at a calibration station 150 which preferably uses a low-field NMR spectrometer 155 to transmit RF pulses to surface coils 160 positioned proximate to the hyperpolarized gas sample. The spectrometer then receives at least one signal 165 back corresponding to the hyperpolarized gas which are processed to determine the polarization level of the hyperpolarized gas (preferably contained in a single dose patient delivery vessel). As shown, the calibration station 150 preferably includes a set of Helmholtz coils 152 (preferably of about 24 inches in diameter) to provide the low magnetic field and a (NMR) surface coil 170 (preferably sized and configured at about 1 inch in diameter and with about 350 turns). The surface coil 170 sits on a platform 172 to preferably position the surface coil 170 in the center of the Helmholtz coils 152. The term “low field” as used herein includes a magnetic field under about 100 Gauss. Preferably, the calibration station is configured with a field strength of about 5-40 gauss, and more preferably a field strength of about 20 gauss. Accordingly, the corresponding ³He signal frequency range is about 16 kHz-128 KHz, with a preferred frequency of about 64 kHz. Similarly, the ¹²⁹Xe signal frequency range is about 5.9 kHz-47 kHz, with a preferred signal frequency of about 23.6 kHz.

[0181] Preferably, the container 250 is positioned on the top surface of the surface coil 170 and substantially in the center of the Helmholtz coils 152. Generally described, in operation, a selected RF pulse (of predetermined pulse, frequency, amplitude, and duration) is transmitted from the NMR device 155 to the surface coil 170. The frequency corresponds to the field strength of the magnetic field and the particular gas, examples of which are noted above. This RF pulse generates an oscillating magnetic field which misaligns at least some of the hyperpolarized ³He or ¹²⁹Xe nuclei from their static magnetic field alignment position. The misaligned nuclei start processing at their associated Larmour frequency (corresponding to pulse frequency). The precessing spins induce a voltage in the surface coil which can be processed to represent a signal 165. The voltage is received back (typically amplified) at the computer and the signal fits an exponentially decaying sinusoid pattern. As shown, the signal 165 received back at the computer is the Fourier transform of the received signal. The peak-to-peak voltage of this signal is directly proportional to polarization (using a known calibration constant). The computer can then calculate the polarization level, and generate calculated preferred use dates and times associated with desired polarization levels. As will be recognized by those of skill in the art, other calibration or hyperpolarization level determination methods can also be employed and still be within the product identification and calibration or product-use or expiration determination methods contemplated by the present invention. For example, detecting the minute magnetic field generated by the polarized ³He spins. Also, as shown in FIG. 15, a purge gas cylinder 177 and associated vacuum and purge equipment 178 are positioned proximate to the calibration station. In one preferred embodiment, the purge and vacuum equipment are positioned on or proximate to the calibration station so that the container can be cleaned (evacuated and pure-gas purged) at the calibration station 150 prior to the calibration. Thus, the calibration station can advantageously be combined with a filling and cleaning station. For example, a rigid transport vessel can transport the hyperpolarized gas from a hyperpolarization site to the calibration station at a use site. The delivery container 250 can be cleaned at the calibration station (or pre-cleaned as discussed above). The gas can be extracted from the transport container into the delivery container 250 right at the calibration station, preferably according to one of the methods of the instant invention. The extracted gas now captured in the container 250 can be easily and instantly measured or identified/calibrated as to its efficacy or hyperpolarization level and marked for instant or future use.

[0182] The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. In the claims, means plus function clauses, where used, are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be within the scope of the appended claims. The invention is defined by the following claims with equivalents of the claims to be included therein. 

That which is claimed is:
 1. A method of meting a quantity of hyperpolarized gas into a container, comprising the steps of: providing an enclosed sealable gas flow path, the gas flow path extending between a hyperpolarized gas source and a gas syringe, and between the gas syringe and a sealable container different from the hyperpolarized gas source, wherein the gas syringe has a translatable plunger held therein and a port configured to receive gas into and expel gas from the syringe; releasing a quantity of hyperpolarized gas in gaseous form from the hyperpolarized gas source such that it flows into the gas flow path; directing the hyperpolarized gas in the gas flow path into the syringe; translating the plunger a distance in the syringe away from the port in response to the quantity of hyperpolarized gas received therein; and advancing the plunger a desired distance in the syringe toward the port to direct a desired quantity of hyperpolarized gas in gaseous form from the syringe into the gas flow path and into the sealable container, thereby meting a desired amount of the hyperpolarized gas into the sealable container.
 2. A method according to claim 1, further comprising directing a quantity of non-polarized buffer gas into the syringe prior to directing the hyperpolarized gas therein such that the non-polarized buffer gas is held in the chamber during the step of directing the hyperpolarized gas therein and the plunger is translated a first distance in the syringe away from the port in response to the quantity of non-polarized gas received therein.
 3. A method according to claim 2, wherein the non-polarized buffer gas is suitable for in vivo administration.
 4. A method according to claim 2, wherein the combined quantity of non-polarized gas and hyperpolarized gas received in the first syringe in gaseous form is in the range of about 20 milliliters to 2 liters.
 5. A method according to claim 2, further comprising the step of preconditioning the first syringe and the sealable container to remove impurities therefrom.
 6. A method according to claim 2, further comprising concurrently expelling both the hyperpolarized gas and non-polarized gas into a receiving container so as to define a pharmaceutical grade dose mixture having a known volume and a known ratio of hyperpolarized gas to buffer gas in the mixture.
 7. A method according to claim 2, wherein the sealable container is sized and configured to hold a quantity of hyperpolarized gas suitable for dispensing as a single dose to a patient.
 8. A method according to claim 2, further comprising the step of leak checking the gas flow path for air leaks prior to the step of directing the hyperpolarized gas into the syringe.
 9. A method according to claim 2, further comprising the step of generating a substantially homogeneous magnetic holding field proximate the first syringe.
 10. A method according to claim 2, wherein said advancing step includes advancing the plunger to expel substantially all of the non-polarized gas and hyperpolarized gas from the syringe.
 11. A method according to claim 1, wherein said method further comprises the steps of: directing a quantity of buffer gas into the first syringe; and holding the buffer gas therein so that a desired quantity of buffer gas remains in the chamber during the step of directing the hyperpolarized gas into the syringe.
 12. A method according to claim 11, wherein the buffer gas comprises at least one of the gases selected from the group consisting of helium, nitrogen, and argon.
 13. A method according to claim 6, wherein the pharmaceutical grade hyperpolarized gas mixture dose quantity is from about 100 milliliters-1.5 liters, and wherein the concentration of hyperpolarized gas therein is from about 10%-90%.
 14. A method according to claim 13, wherein the hyperpolarized gas concentration is between about 20%-99%.
 15. A method according to claim 2, further comprising directing a second quantity of buffer gas into the syringe while the first quantity of buffer gas and the hyperpolarized gas are held therein.
 16. A method of dispensing hyperpolarized gas mixtures into a container, comprising: providing an enclosed sealable gas flow path, the gas flow path including an inlet flow path extending between a source of hyperpolarized gas and a gas syringe having a gas holding chamber and a source of non-polarized buffer gas and the gas syringe, and an outlet flow path extending between the syringe and a sealable receiving container, wherein the gas syringe has a translatable plunger held in the chamber and a port configured to receive gas into and expel gases from the syringe; directing a quantity of non-polarized buffer gas to travel through the inlet flow path, through the port of the gas syringe, and into the chamber of the gas syringe causing the plunger to translate a first distance away from the port of the gas syringe; then directing the hyperpolarized gas to travel through the inlet flow path, through the port of the gas syringe, and into the chamber of the syringe causing the plunger to translate a second distance away from the port of the gas syringe, wherein the non-polarized buffer gas is held in the syringe while the hyperpolarized gas is directed therein; and advancing the plunger a desired distance in the syringe toward the port to direct the hyperpolarized gas in gaseous form and the non-polarized buffer gas to exit together from the syringe into the outlet gas flow path and into the receiving container, thereby meting an amount of hyperpolarized gas mixture into the receiving container.
 17. A method according to claim 16, wherein the outlet flow path is configured so that the receiving container is directly attached to syringe.
 18. A method according to claim 16, wherein the outlet flow path is configured so that the receiving container is indirectly attached to the syringe.
 19. A method according to claim 16, wherein the buffer gas comprises at least one of the gases selected from the group consisting of helium, nitrogen, and argon.
 20. A method according to claim 16, wherein said step of advancing metes a hyperpolarized gas mixture dose amount of from about 100 ml-1.5 liters into the receiving container.
 21. A method according to claim 20, wherein the hyperpolarized gas mixture dose amount includes a concentration of hyperpolarized gas therein from about 10%-99%.
 22. A method according to claim 21, wherein the hyperpolarized gas is ³He and the concentration in the dose mixture is between about 10-40%.
 23. A method according to claim 16, wherein the buffer gas source is a gas cylinder comprising a high purity grade nitrogen gas in fluid communication with the syringe.
 24. A method according to claim 21, wherein the receiving container is sized and configured to hold a dose mixture quantity of hyperpolarized gas and buffer gas suitable for dispensing in vivo as a single inhalation-administered dose to a patient.
 25. A method according to claim 21, further comprising the step of generating a substantially homogeneous magnetic holding field proximate the syringe during the step of directing the hyperpolarized gas therein.
 26. A method according to claim 21, wherein the syringe comprises graduation marks or externally visual indicia of volume, and said step of directing a quantity of non-polarized buffer gas into the gas syringe is carried out until the plunger translates a first distance away from the port of the gas syringe corresponding to a selected indicia or graduation mark, and wherein the step of directing the hyperpolarized gas into the chamber of the syringe is carried out until the plunger translates a second distance away from the port of the gas syringe to a selected indicia or graduation mark and halting the movement of the plunger substantially thereat.
 27. A method of dispensing a meted quantity of gaseous hyperpolarized gas in a gas mixture, comprising: pre-filling a gas syringe with a first quantity of non-polarized buffer gas; then filling the gas syringe with a second quantity of hyperpolarized gas while the non-polarized buffer gas is held therein; and expelling both the non-polarized gas and the hyperpolarized gas from the syringe thereby dispensing out a meted quantity of hyperpolarized gas in a gas mixture.
 28. A method according to claim 27, wherein the buffer gas comprises at least one of the gases selected from the group consisting of helium, nitrogen, and argon suitable for in vivo administration to a patient.
 29. A method according to claim 28, wherein said step of expelling metes a hyperpolarized gas mixture dose amount of from about 100 ml-1.5 liters into a patient delivery container.
 30. A method according to claim 29, wherein the hyperpolarized gas mixture dose amount includes a concentration of hyperpolarized gas therein from about 10%-99%.
 31. A method according to claim 29, further comprising generating a magnetic field proximate to the syringe to provide a magnetic holding field about the syringe.
 32. A method according to claim 31, wherein said magnetic field generator is an electromagnet.
 33. A method according to claim 31, wherein said magnetic field generator is an arrangement of a plurality of discrete permanent magnets.
 34. A method according to claim 27, wherein said steps of pre-filling and filling are carried out in quantities sufficient to define single patient-sized dose quantities of the hyperpolarized gas mixture in a range of between about 100 ml-1.5 liters.
 35. A method of preparing a hyperpolarized gas extraction system to inhibit the presence of oxygen therein, comprising: introducing a quantity of inert noble purge gas into a gas flow path of a gas extraction system; evacuating the flow path of the gas extraction system; repeating the purging and evacuating steps; then introducing additional purge gas into the gas flow path of the extraction system until the pressure therein is at about or above atmospheric pressure so as to inhibit oxygen from entering therein; and introducing a desired quantity of hyperpolarized gas in the flow path of the extraction system.
 36. A method according to claim 35, further comprising holding a quantity of the purge gas in the extraction system while the system is waiting to commence extracting hyperpolarized gas prior to the step of introducing the hyperpolarized gas in the flow path.
 37. A method according to claim 35, wherein the step of introducing additional purge gas into the flow path is carried out so that the pressure is above atmospheric pressure.
 38. A method according to claim 35, further comprising evacuating the purge gas prior to commencing the step of introducing the hyperpolarized gas.
 39. A method according to claim 38, further comprising introducing a desired quantity of buffer gas in the flow path of the extraction system prior to the step of introducing the hyperpolarized gas. 